The Syrian government said it had no evidence of a strike.
The strike would most likely have involved F-15 or F-16 aircraft from the Israeli defence forces. They can be armed with laser-guided bombs and with air-launched missiles.
One American official said they understood the Israeli planes had not entered Syrian air space, suggesting they made use of long-range satellite-guided missiles for the attack.
The strike is not the first time Israel has hit targets in Syria. In January this year, Israel bombed a convoy in the country, apparently hitting weapons destined for Hezbollah, the militant group based in Lebanon which has been behind attacks on Israel from its bases in Lebanon.
In 2007, Israeli jets bombed a suspected nuclear reactor site along the Euphrates River in northeastern Syria, an attack that embarrassed the Assad regime. It also led to Assad building up air defences with Russian technology.
Previously Israel launched a bombing raid on Sudan, targeting what its intelligence officers had concluded was a factory making rockets which were being used to attack the country from the Gaza Strip.
Israel is particularly concerned that Hezbollah, the Lebanon-based militant group, could acquire new and even more dangerous weapons from the crumbling Assad regime.
Assad is known to have chemical weapons, and is now facing mounting scrutiny over whether those have been deployed against Syrian civilians, and on what scale.
Confirmation of the large-scale use of the weapons would increase pressure on western countries to intervene, and Assad has been warned directly by Barack Obama, the American president, that evidence of the use of chemical weapons as a "game-changer" that would have "enormous consequences".
However Philip Hammond, the Defence Secretary, warned earier this week as he prepared for talks in Washington with Chuck Hagel, his American counterpart, that proving the use of such weapons was difficult.
"The confidence that we are seeking degrades over time, and in order to have a properly measured chain of custody we would need to obtain samples after an[other] incident," he said in a briefing at the British embassy.
"If chemical weapons use continues, albeit on a small scale, then I am confident that we can detect further use. The regime will now be focused on the fact that the west will be looking for evidence."
In America, Mr Obama has rejected calls to step up involvement in the Syrian conflict, including suggestions of enforcing a no-fly zone, which would rob Assad of his major tactical advantage over the rebels, the use of air superiority. Syria has used planes and attack helicopters in the civil war, which is now estimated to have claimed 70,000 lives.
Hours after the first reports of the strike by Israel, he said that he could not foresee a scenario in which American ground forces would be deployed to the country.
However, Mr Hagel had warned on Thursday that the American government was re-considering its opposition to arming rebels and on the same day Mr Obama, speaking in Mexico, said: "We want to make sure that we look before we leap and that what we're doing is actually helpful to the situation as opposed to making it more deadly or more complex."
The strike would most likely have involved F-15 or F-16 aircraft from the Israeli defence forces. They can be armed with laser-guided bombs and with air-launched missiles.
One American official said they understood the Israeli planes had not entered Syrian air space, suggesting they made use of long-range satellite-guided missiles for the attack.
The strike is not the first time Israel has hit targets in Syria. In January this year, Israel bombed a convoy in the country, apparently hitting weapons destined for Hezbollah, the militant group based in Lebanon which has been behind attacks on Israel from its bases in Lebanon.
In 2007, Israeli jets bombed a suspected nuclear reactor site along the Euphrates River in northeastern Syria, an attack that embarrassed the Assad regime. It also led to Assad building up air defences with Russian technology.
Previously Israel launched a bombing raid on Sudan, targeting what its intelligence officers had concluded was a factory making rockets which were being used to attack the country from the Gaza Strip.
Israel is particularly concerned that Hezbollah, the Lebanon-based militant group, could acquire new and even more dangerous weapons from the crumbling Assad regime.
Assad is known to have chemical weapons, and is now facing mounting scrutiny over whether those have been deployed against Syrian civilians, and on what scale.
Confirmation of the large-scale use of the weapons would increase pressure on western countries to intervene, and Assad has been warned directly by Barack Obama, the American president, that evidence of the use of chemical weapons as a "game-changer" that would have "enormous consequences".
However Philip Hammond, the Defence Secretary, warned earier this week as he prepared for talks in Washington with Chuck Hagel, his American counterpart, that proving the use of such weapons was difficult.
"The confidence that we are seeking degrades over time, and in order to have a properly measured chain of custody we would need to obtain samples after an[other] incident," he said in a briefing at the British embassy.
"If chemical weapons use continues, albeit on a small scale, then I am confident that we can detect further use. The regime will now be focused on the fact that the west will be looking for evidence."
In America, Mr Obama has rejected calls to step up involvement in the Syrian conflict, including suggestions of enforcing a no-fly zone, which would rob Assad of his major tactical advantage over the rebels, the use of air superiority. Syria has used planes and attack helicopters in the civil war, which is now estimated to have claimed 70,000 lives.
Hours after the first reports of the strike by Israel, he said that he could not foresee a scenario in which American ground forces would be deployed to the country.
However, Mr Hagel had warned on Thursday that the American government was re-considering its opposition to arming rebels and on the same day Mr Obama, speaking in Mexico, said: "We want to make sure that we look before we leap and that what we're doing is actually helpful to the situation as opposed to making it more deadly or more complex."