Live coverage of events, after Israeli commandos storm a convoy of boats carrying aid to Gaza, showing latest developments with breaking news and comment from BBC correspondents. All times BST.
With the UN Security Council preparing to meet in New York, we close our live coverage page.
The BBC's Barbara Plett at the UN reports that the Turkish foreign minister, not the Turkish prime minister, will attend the meeting.
US President Barack Obama told Israeli Prime Minister Benjamin Netanyahu on the phone of his regret over the people killed in the raid, the White House says.
"The president expressed deep regret at the loss of life in today's incident, and concern for the wounded, many of whom are being treated in Israeli hospitals. The president also expressed the importance of learning all the facts and circumstances around this morning's tragic events as soon as possible."
He added he understood the Israeli prime minister's decision to return immediately to Israel to deal with the events, and said they agreed to reschedule their meeting at the first opportunity.
In his first public comments on the incident, Israeli Prime Minister Benjamin Netanyahu says Israel "regrets" the loss of life in the raid:
"We told the flotilla of ships and said, you can take all your cargo, put it in our port of Ashdod and we'll just ferret out, if there are any war materials and the rest will go through. We succeeded doing this peacefully with five of the six ships. The sixth ship, the largest, which had hundreds of people on it, not only did not co-operate in this effort, peacefully, they deliberately attacked the first soldiers that came on the ship.
"They were mobbed. They were clubbed, they were beaten, stabbed. There was even a report of gunfire and our soldiers had to defend themselves, defend their lives or they would have been killed."
Nato ambassadors are to hold emergency talks on Tuesday at Turkey's request to discuss the raid, spokesman James Appathurai is quoted as saying by the AFP news agency.
1657: The BBC's Jon Donnison in Gaza City says:
At a Hamas-organised rally at the port in Gaza City, there seems to be genuine anger from the politicians, and among ordinary people a feeling of relief and surprise at the attention the story is getting.
But after a day of drama for those ordinary Gazans, the blockade goes on; and whoever is blamed, and some here blame Hamas as well as Israel, that means continued hardship, shortages and difficulties rebuilding their lives after years of conflict.
Turkish Prime Minister Tayyip Erdogan accuses Israel of "state terrorism" over the raid.
"This action, totally contrary to the principles of international law, is inhumane state terrorism. Nobody should think we will keep quiet in the face of this."
Hamas's high representative in Beirut, Osama Hamdan, tells the BBC there is international pressure on Israel over the raid.
"We hope that this may change the political climate, it may convince Israel that the people all over the world are trying to break down the siege. The Israelis are talking about weapons on those ships - I believe they are lying."
1610: The BBC's Natalia Antelava in Beirut, Lebanon, says:
Events in Gaze provoked angry reactions from people and politicians across the Arab world. Lebanon, which currently holds the presidency of the UN Security Council, is calling on an emergency session to discuss what happened.
Palestinian groups in both Syria and Lebanon have staged sit-ins and protest rallies. At the demonstration in front of the UN building in Beirut, many said they were outraged by the events.
All of this certainly adds fuel to the current atmosphere of nervousness and anger in the region. Israel and Washington have recently accused Syria of transferring long-range scud missiles to the Lebanese militant group Hezbollah. Lebanon's prime minister says these accusations are nonsense, but Hezbollah itself claims to have military capability to hit targets deep inside the Israeli territory.
German Chancellor Angela Merkel says she has urged Israel and Turkey to ensure there was no escalation of violence in the Middle East following the raid.
She said she had spoken by telephone with Israeli Prime Minister Benjamin Netanyahu and his Turkish counterpart Tayyip Erdogan.
"I made... my profound concern clear and noted that everything must be done in this difficult situation to ensure that there is no escalation."
Hanan Ashwari from the Palestinian Legislative Council calls on the UN Security Council to punish the Israelis.
She tells the BBC: "I think for the first time Israel has to be held accountable; morally accountable, legally accountable, politically accountable and judicially accountable.
"I think the Security Council... has to take serious decisions, has to lift the cover of impunity - particularly that which is provided by the US...
"They have to take serious resolutions pertaining to lifting the blockade and ending the occupation."
1526: The BBC's Wyre Davies in Ashdod, Israel, says:
The ships have been being brought in one by one. Three have come in so far. We've not been given access to the crews or the activists - the Israelis are keeping a very tight rein on them.
It's very tense in Ashdod. Arabic TV crews have been harassed by pro-Israeli demonstrators. There are dozens of right-wingers voicing support for what happened last night and heckling the international media.
The Israeli authorities have told us they're going to process the activists - anyone injured will be treated, the rest will be deported.
Any of the aid that clears the Israeli checks will be transferred into Gaza, but they have said that if certain things are found to be contraband they will be excluded.
A spokesman for the Israeli Defense Forces, Afikhai Adrei, told the BBC Arabic service that one of the activists snatched guns from Israeli marines during the operation and opened fire.
"Those who met the Israeli army personnel with knifes are not peace advocates, they are not harmless.
"There is a simple military explanation: when these people take a weapon from one of the Israeli soldiers and start shooting, then the Israeli soldiers have the right to defend themselves."
Israeli Prime Minister Benjamin Netanyahu has cancelled his plans to meet US President Barack Obama in Washington on Tuesday, an Israeli statement said.
Mr Netanyahu will shortly leave Canada, where he has been meeting government leaders, his office said.
The latest statement contradicts earlier reports.
The UN Security Council is to meet at 1800. The Turkish prime minister is expected to attend.
Israeli Prime Minister Benjamin Netanyahu expressed his "full backing" for Israeli army forces, according to an Israeli military statement.
1351: The BBC's Middle East editor Jeremy Bowen says:
Israel's alliances in the eastern Mediterranean have been damaged.
It used to have close relations with Turkey, where much of the flotilla was organised, but now relations are in crisis, deepening a rift that started with the Gaza war last year. Greece has called off joint military exercises.
Israel's Prime Minister Benjamin Netanyahu was preparing for a long-awaited meeting with US President Obama, which he was likely to present as a sign that Israel has not been harmed by the row he's been having with the White House over building for Jews in the occupied territories.
Now the visit will be dominated by redoubled international criticism of Israel's blockade of Gaza and the perception that Israeli troops tend to shoot first and ask questions later.
Israeli Prime Minister Benjamin Netanyahu will remain in Canada and travel to Washington for talks with US President Barack Obama as planned on Tuesday, Israeli spokesman Mark Regev told Canadian media, contradicting earlier reports.
"Even on a tough day, on a day when everyone is up in arms on this issue, it's very important that we sit down with friends and allies and discuss issues of mutual concern," Mr Regev said told CBC News.
Middle East peace envoy Tony Blair expressed his "deep regret and shock" at the loss of life on the flotilla and called for an investigation.
"Once again I repeat my view that we need a different and better way of helping the people of Gaza and avoiding the hardship and tragedy that is inherent in the present situation," he said.
1334: The BBC's Dale Gavlak in Amman, Jordan, says:
A strong US ally in the Middle East, moderate Jordan condemned the attack, calling it a heinous crime.
The foreign ministry summoned the Israeli ambassador to lodge a strongly worded letter of protest, but demonstrators want tougher action taken.
That's because Jordan has borne the brunt of each conflict between Israel and the Arabs, seeing hundreds of thousands of Palestinians fleeing across its border and disrupting its delicate demographic balance.
1323: Andy David from the Israeli foreign ministry tells the BBC in Ashdod, Israel:
We have to understand what happened, We are talking about an organisation, the IHH, who was on this ship... [which] is a radical Muslim organisation with ties to al-Qaeda and to Hamas.
They were there not to deliver peacefully humanitarian aid. They were there waiting with knives, with metal bars. They were there to attack.
The other option was for the commandos to use more force, and then there would be criticism for excessive force.
They were given orders, specific orders not to use weapons, only if they were under life threat. That was exactly the case. That's why they were using those weapons.
Egyptian President Hosni Mubarak condemns Israel's "excessive and unwarranted use of force" in its raid on the flotilla.
Egypt has summoned the Israeli envoy in Cairo, reports say.
In the first reaction from Washington, a White House spokesman expressed US concern at the deaths and injuries caused in the raid.
"The United States deeply regrets the loss of life and injuries sustained, and is currently working to understand the circumstances surrounding this tragedy," said White House spokesman William Burton.
EU foreign affairs chief Catherine Ashton said she had called Israel's top diplomat to express concern after the raid.
"During the course of this morning I have spoken to Minister [Avigdor] Lieberman, the foreign minister of Israel. I expressed my deepest concern about the tragedy that has happened. I said that we needed an inquiry by Israel into the circumstances."
1241: The BBC's Jon Donnison in Gaza City says:
Here in Gaza City, demonstrators have gathered at the port, waving banners and chanting slogans to protest against Israel's actions.
The aim of this flotilla was to focus attention on Israel's three-year blockade of Gaza; it has certainly done that, but at the expense of many lives.
UK Foreign Secretary William Hague said he "deplored" the loss of life on the flotilla and was seeking more information and urgent access to any UK nationals.
In a statement, he said: "There can be no better response from the international community to this tragedy than to achieve urgently a durable resolution to the Gaza crisis.
"I call on the government of Israel to open the crossings to allow unfettered access for aid to Gaza, and address the serious concerns about the deterioration in the humanitarian and economic situation and about the effect on a generation of young Palestinians."
The Vatican says it feels "deep sadness" at the Israeli raid.
"This is a very painful fact, in particular because of the loss of human lives," said chief Vatican spokesman Father Federico Lombardi.
French President Nicolas Sarkozy accuses Israel of a "disproportionate use of force".
UN Secretary General Ban Ki-moon says he is "shocked by reports of killings and injuries" on the flotilla and says it is vital that Israel carries out a full investigation.
Israeli Prime Minister Benjamin Netanyahu is to cut short an official trip to Canada and Washington, Israeli radio reports.
Turkish Prime Minister Recep Tayyip Erdogan is to cut short an official trip to Latin America to deal with the political fallout of the Israeli action.
Turkey says it is recalling its ambassador from Tel Aviv.
The BBC's Natalia Antelava in Beirut says many people have taken to streets in Beirut and are protesting in front of the United Nations building.
Ambassadors from European Union's 27 member states are to hold emergency talks in Brussels on the Israeli operation.
1105: The BBC's Tim Franks in Jerusalem says:
More details are emerging about the Israeli version of what happened on the boat.
Yochanan Plessner, member of the Israeli parliament and former navy commando himself, says that the moment Israeli commandos boarded the boat they were attacked by spikes, metal rods, and live ammunition.
He said: "They were actually thrown down the different levels of the ship. Basically the Israeli soldiers who came for policing type activity were lynched."
Turkey's foreign ministry calls for an emergency meeting of the United Nations Security Council over Israel's military operation.
Frank Barat of the Russell Tribunal for Palestine tells the BBC he has several friends onboard ships in the flotilla and is concerned for their welfare.
Briton Sarah Colborne, the director of the Palestine Solidarity campaign in London was last heard from at 2300 on Sunday, speaking live via a webcast from the Turkish ship that was intercepted.
Mr Barat says another friend, Ewa Jasiewicz, who is part of the Free Gaza movement, was on board one of the smaller ships.
Nabil Amr, an adviser to Palestinian president Mahmoud Abbas, condemns Israel's actions:
"The Palestinian Authority cannot let what happened go unnoticed.
"What happened is merely an international cry that does not carry any aggression or a violation of any borders; it is only a strong humanitarian call addressed to the world to end this unjust siege against our people in the Gaza Strip," he tells broadcaster al-Jazeera.
Wallander author Henning Mankell is among those believed to be on board the ships to Gaza.
Israel's Channel 10 TV says 19 activists were killed and 26 wounded.
1030: The BBC's Malcolm Brabant in Athens says:
Greece has withdrawn from joint military exercises with Israel in protest at the attack on the Gaza flotilla.
Athens has also barred the head of the Israeli air force from flying to Greece.
The Greeks have long had warm relations with the Palestinians and are furious with the Israelis for carrying out this raid in international waters.
The Israeli ambassador to Athens was called into the foreign ministry to provide an explanation. The deputy foreign minister, Dhimitris Droutsas, demanded assurances about the wellbeing of 30 Greeks who were on board ships in the flotilla.
Mr Yahya was told in no uncertain terms that Greece held Israel responsible for their safety. One of the vessels currently being escorted by the Israelis towards the port of Ashdod is sailing under a Greek flag.
French Foreign Minister Bernard Kouchner says he is "deeply shocked" by the Israeli action and calls for an inquiry.
The first of the six ships in the flotilla dock in Ashdod, Israel.
Thousands of Turkish protesters march in Istanbul to denounce Israel.
Turkish foreign ministry warns Israel of irreparable damage to bilateral ties.
"This deplorable incident, which took place in open seas and constitutes a fragrant breach of international law, may lead to irreparable consequences in our bilateral relations," a statement read.
The Arab League calls an emergency meeting on 1 June to discuss Israel's "terrorist act" against the flotilla.
Sweden summons the Israeli ambassador to Stockholm over the "unacceptable" action.
The Israeli Deputy Foreign Minister, Daniel Ayalon, blamed the organisers for the violence, saying they were linked to terrorist organisations.
"The armada of hate and violence in support of Hamas terror organisation was a premeditated and outrageous provocation.
"The organisers are well known for their ties with global Jihad, al-Qaeda and Hamas. They have a history of arms smuggling and deadly terror.
"On board the ship we found weapons prepared in advance and used against our forces. The organisers intent was violent, their method was violent and the results were unfortunately violent. Israel regrets any loss of life and did everything to avoid this outcome."
0900: The BBC's Tim Franks in Jerusalem says:
After the funerals and after the rage Israel will face two big questions: if, as Israeli officials insist, they are happy to channel all this aid into Gaza via Israeli ports - including the building materials which it claims Hamas could put to military ends - then what's the point of the blockade?
And how far can it continue to stick to the line that "there are no shortages in Gaza", when the United Nations, among others, describes the humanitarian situation as "grim" and "deteriorating"?
0845: Audrey Bomse of the Free Gaza movement, which organised the convoy, tells the BBC:
"I can tell you that there were no firearms - all the boats were carefully inspected by the government before they left the port of departure.
"You can't hide a firearm; I suppose you can hide a knife, but there's no evidence there was shooting, there was live streaming coming from the boats.
"You don't see any fire going past the Israelis, you see them coming out of helicopters and shooting immediately."
0830: The BBC's Wyre Davies in Ashdod, Israel, says:
An Israeli army spokesman said the activists refused an order not to go to Gaza with their boats laden with humanitarian aid and instead dock at the Israeli port of Ashdod.
The army says its troops were attacked by the activists with axes, knives and firearms.
At least four Israeli marines were injured, said a spokeswoman, including one who was shot when his gun was snatched by an activist.
There's now a state of alert across Israel.
Israeli spokesman Mark Regev speaks to the BBC's Today programme:
0800: The BBC's Jon Donnison in Gaza City says:
Israel had warned it was going to use limited force to stop the flotilla. It seems to have used more than that.
Television pictures from on board the ships show Israeli armed commandos storming the boats.
You can hear what sounds like gun shots and a number of people can be seen lying on the deck, apparently injured.
It took place around 60km out to sea in international waters. An Israeli government minister expressed regret for any loss of life.
Israel has said it will tow the ships to Ashdod where a special passport and detention centre has been set up.
It says from there the activists will be deported.
Hamas leader Ismail Haniya says of the activists: "You were heroes, whether you reached [Gaza] or not."
0730: The BBC's Jonathan Head in Istanbul, Turkey, says:
Within hours of the first clashes between Israeli forces and the Gaza bound convoy the Turkish government issued a strongly-worded condemnation of the Israeli actions.
Once again Israel has shown that it ignores human rights and peaceful initiatives, read the statement from the foreign ministry.
It accused Israel of violating international law by using such force on the high seas, and said its actions could have irrevocable consequences for relations with Turkey.
The main organiser of the convoy is a Turkish-based Islamic charity and most of the activists on board are Turkish citizens.
If the reports of large numbers of casualties are confirmed, relations between Turkey and Israel, already badly strained over the blockade of Gaza, will plunge to a new low.