Israel 'ready for escalation' of Gaza conflict
At least 15 people have been killed in the Gaza Strip as Israel launches a major air and sea offensive against the militant group Hamas.
It comes in response to Hamas firing more than 130 rockets at Israeli cities since Monday night.
On Tuesday evening, militants launched several rockets towards Jerusalem but did not hit the city, Israeli police said.
Israel has warned it may send ground troops into Gaza to stop the attacks.
It has authorised the call-up of up to 40,000 military reservists. Hundreds of reservists have already been drafted to bolster forces around Gaza.
Hamas said all Israelis were now targets.
Palestinian Authority President Mahmoud Abbas demanded that Israel immediately stop the raids on Gaza and appealed for calm.
The Israeli military said it had targeted some 50 "terror sites" on Tuesday, in response to the missiles being fired from Gaza.
It confirmed that aircraft and naval vessels had targeted militant compounds, rocket launchers and other infrastructure in Gaza, which is dominated by Hamas and until recently was governed by it.
Missiles struck the homes of several Hamas operatives who Israel claimed were involved in firing rockets, and what it said was a command centre located in a civilian building.
Among those killed in the raids were four Hamas members who died in Gaza City when their car was struck. One of the dead was Mohammed Shaaban, a senior militant.
Later, the home of a Hamas leader in the southern city of Khan Younis was hit, killing six people. Health ministry spokesman Ashraf al-Qudra said two teenage boys were among those killed. Another 25 people were injured.
A Hamas spokesman condemned the air strike, calling it a "horrendous war crime".
The militant group later said it had launched several rockets at Jerusalem, Tel Aviv and other Israeli cities on Tuesday.
Israeli officials said none of the missiles had reached their target.
At the scene: Yolande Knell, BBC News, Beit Lahiya, Gaza Strip
There have been several loud thuds in the northern Gaza Strip as Israeli military planes hit targets here.
The biggest strikes shake the ground and send up huge plumes of smoke.
A woman ran past us with three small children - all were crying and in shock. Nearby a house had just been damaged by an Israeli air strike. Two ambulances whizzed by carrying away the injured.
"[Militants] used to launch rockets from here. [The Israeli military] targeted these houses several times," a local man told us.
It is extremely tense on the streets and most residents - observing the dawn-to-dusk fast for the Islamic holy month of Ramadan - are staying in their homes.
At the scene: James Reynolds, BBC News, Sderot, Israel
Outside a bomb shelter, we heard a loud, dull boom. A small crowd squinted and pointed to a puff of white smoke in the sky.
"It's an interception," said one man, suggesting that Israel's Iron Dome missile defence system had knocked a Hamas rocket out of the sky.
"I'm not happy," said another man, "because even if there's an interception, debris still falls."
At the time of the explosion, Israel's President-elect, Reuben Rivlin, was inside the underground shelter, giving a briefing.
"Is Israel preparing for war with Hamas?" I asked him.
"We are in war with Hamas because Hamas has declared war on us," he replied. "We are in war - not because of us - because of Hamas."
A little later, Mr Rivlin visited schoolchildren, taking summer classes in a fortified classroom which looked like a bunker.
"We have to hit Hamas hard," said a rabbi.
On the roof of the religious school across the road, a group of students looked out towards Gaza in the distance.
'Intolerable' rocket fire
The White House issued a statement on Tuesday condemning the rocket fire and expressed support for Israel's right to defend itself "against these vicious attacks".
Israeli Prime Minister Benjamin Netanyahu has instructed the country's military to prepare for every scenario, including a ground offensive.
"We are preparing for a battle against Hamas which will not end within a few days," his Defence Minister, Moshe Yaalon, said in a statement.
He said Israel was "prepared to extend the operations with all means at our disposal in order to keep hitting Hamas".
The Israeli military said it had received provisional government approval to call up as many as 40,000 reserve soldiers, but had not done so yet.
Spokesman Lt Col Peter Lerner said it was preparing for an "escalation" of the campaign, dubbed "Operation Protective Edge", and would continue its bombardment as long as Israeli citizens were under fire.
The government has declared a state of emergency in southern Israel.
In cities and towns within 40km (24 miles) of Gaza, summer camps and schools have been instructed to close and residents have been encouraged to stay near their homes.
The sudden escalation comes just days after suggestions of a truce from both Israel and militant groups in Gaza.
Tensions spiked last week with the murders of three young Israelis in the occupied West Bank and a Palestinian teenager in Jerusalem.
Israel says Hamas was behind the abduction and murder of the Israeli youths - a claim it denies.
A day after their funerals, the Palestinian was abducted in East Jerusalem and murdered. Police have arrested six Jewish suspects and say it seems the 16-year-old was killed because of his nationality.