White House warns Syria over 'weapons to Hezbollah'
The White House has warned Syria not to transfer weapons to Hezbollah in neighbouring Lebanon.
The warning came amid contradictory claims of an Israeli strike in Syria.
Syria says Israeli war planes bombed a military research centre north-west of Damascus, but the US and others say lorries carrying weapons bound for Lebanon were hit.
Israel has maintained silence about the incident, but Syria has made a formal complaint to the UN.
Damascus says it reserves the right to defend itself, while its allies Russia and Iran have strongly denounced the attack.
- Jamraya Centre: Reported scientific research centre responsible for developing chemical weapons
- Weapons convoy: Lorries carrying Russian-made SA-17 anti-aircraft missiles to Hezbollah bases in Lebanon
The Syrian army statement about the incident, carried on state media, said Israeli fighter jets had carried out a direct strike on a scientific research centre in Jamraya, killing two people and wounding five.
But a US official told the BBC the target was a convoy carrying SA-17 surface-to-air missiles. Some rebel groups have said they targeted the Jamraya centre.
Israel has declined to comment.
The latest developments have struck a country in turmoil. Syrian President Bashar al-Assad continues to cling to power despite a 22-month conflict that has killed more than 60,000 people.Syria protest
White House deputy national security adviser Ben Rhodes did not confirm details of Israel's raid itself, but had a warning to issue to Syria.
"Syria should not further destabilise the region by transferring weaponry to Hezbollah," he said.
Amid a welter of contradictory reports and rumours, it seems to be established that Israel did mount a lightning air strike inside Syria, despite complete silence from Israeli officials.
That is their normal practice on such occasions. Additionally, they know that intervening in the complex Syrian internal conflict carries big political risks, not least being accused of teaming up with the rebels.
That is exactly what has happened, with Syria and its allies Iran and Hezbollah saying the attack exposed complicity between Israel, the West, and the Syrian opposition.
Israel knows that intervening in such a way would be likely to embarrass the rebels and strengthen President Assad politically. Whatever prompted it to act must have been compelling enough to override that consideration.
Israel has made it clear that arms transfers from Syria to Hezbollah would constitute a red line.
Most Western accounts believe such an arms convoy was the target. If the Jamraya complex was instead - or also - hit, as Damascus insists, the Israelis must have suspected that something seriously dangerous was going on there.
News of the attack does not appear to have generated much alarm in Washington, says the BBC's Paul Adams.
Indeed, he says, the presence in Washington of Israel's military intelligence chief suggests the Obama administration may have been told about the raid beforehand.
But Syria's foreign ministry summoned the UN commander in the Golan to deliver a formal protest, saying Israel's action violated the 1974 disengagement agreement between the two sides, who remain technically at war.
A UN observer force has been in place in the Golan since 1974, with the task of providing "an area of separation and for two equal zones of limited forces and armaments on both sides of the area".
"Syria holds Israel and those who are protecting it at the Security Council responsible for the results of the attack and confirms its right to defend its land and sovereignty," Syria said in a letter to the UN, reported by state media.
But Syria itself is hardly in a position to do much, says the BBC's Jim Muir in Beirut.'Unprovoked attacks'
Both Hezbollah and Iran are also under pressure at the moment, and Israel's calculation must be that none of those hostile parties has an interest in triggering a regional conflagration right now, our correspondent says.
Later, the UN Secretary General Ban Ki-moon expressed "grave concern" over reports of Israel's action, and called on all concerned to respect international law.
Syria's allies denounced Israel's action, while Iranian Foreign Minister Ali Akbar Salehi condemned the alleged air strike as an "overt assault based on the West's policy" to undermine stability in Syria.
Russia - a stalwart defender of Syria on the international diplomatic scene despite its warming trade and economic ties with Israel - also took a strong stance.
"If this information is confirmed," said the foreign ministry, "then we are dealing with unprovoked attacks on targets on the territory of a sovereign country, which blatantly violates the UN Charter and is unacceptable, no matter the motives to justify it."
Earlier Syria's ambassador to Lebanon warned Damascus could take a "surprise" decision to retaliate.
Israeli media reaction
"Israel is closer today to confrontation on the northern front more than it has been at any point since the Second Lebanon War." Alex Fishman, Yedioth Ahronoth
"It could be seen as a hint to other countries, like Turkey and the US, that a military attack on Syria to topple the regime may be an option." Zvi Barel, Ha'aretz
"There have been many signs in recent days that winds of war are blowing in the north. But… an attack, which did or did not take place, will not lead to an immediate round of combat in the north." Amir Rapaport, Ma'ariv
"If Israel acted, as foreign publications say, the ball is in Assad's court. The problem is that in the current situation, he has no court and does not have much to lose. A wounded lion is a dangerous lion." Boaz Bismuth,Yisrael Hayom
US Vice-President Joe Biden is travelling to Germany, where he is expected to discuss the situation in Syria with Russian Foreign Minister Sergei Lavrov and the Syrian opposition leader, Moaz al-Khatib.Weapons facility
The Syrian army statement said the Jamraya centre - which was focused on "raising our level of resistance and self-defence" - was damaged in the attack, and specifically denied reports that an arms convoy had been hit.
It said "armed terrorist gangs" - a term the government uses to describe rebel groups - had tried and failed repeatedly to capture the same facility in recent months.
But an opposition activist told the Washington Post that, although there had been two attacks on the centre early on Wednesday, "we did not hear any airplanes... Unless the airplanes were silenced by some technology."
"I mean, is it possible for an air fighter to attack at night, and we don't even hear its sound?"
Some reports suggest the facility could be Syria's Scientific Studies and Research Centre, known by its French acronym CERS, believed to be the state organisation responsible for developing biological and chemical weapons.
Lebanese military and internal security forces say there has been increased activity by Israeli warplanes over Lebanon in the past week, and particularly on Tuesday and the early hours of Wednesday morning.
There is increasing concern in Israel that Syria's chemical weapons could fall into Hezbollah's hands.
Correspondents say Israel is also concerned the Shia militant group could obtain anti-tank and anti-aircraft missiles, thus strengthening its ability to respond to Israeli air strikes.
Israel believes Syria received a battery of SA-17s from Russia after an alleged Israeli air strike in 2007 that destroyed a Syrian nuclear reactor near Deir Ezzor in eastern Syria, analysts say.
Wednesday's reported attack came days after Israel moved its Iron Dome defence system to the north of the country.