Israeli officials have confirmed that the country's airforce launched a strike into Syria, targeting suspected weapons. It comes as the US president Barack Obama almost completely ruled out deploying US troops to Syria.
The officials, speaking on condition of anonymity, say Friday's strike targeted a shipment of missiles bound for the Lebanese militant group Hezbollah.
One official said the target was advanced, long-range ground-to-ground missiles.
CNN television earlier reported that US and Western intelligence agencies were reviewing the information, and that the US did not believe Israeli warplanes entered Syrian airspace to launch the strikes.
There has been no word from Syrian officials or on Syrian state media.
US Republican Senator Lindsey Graham was quoted by the Politico news website as confirming the reports. "Israel bombed Syria tonight," he said, according to Politico, without offering any further details.
Aaron Sagui,, spokesman for the Israeli embassy in Washington, would not comment specifically on the reports.
"What we can say is that Israel is determined to prevent the transfer of chemical weapons or other game-changing weaponry by the Syrian regime to terrorists, especially Hezbollah in Lebanon," wrote said in an email to AP.
Obama: No US troops in Syria
News of the apparent airstrike came amid statements from US President Barack Obama in Costa Rica, where he met with President Laura Chinchilla and other Central American leaders. He was asked how he would respond if the Syrian regime is proven to have used chemical weapons.
The US president - who has spent much of his time in power winding down wars in Iraq and Afghanistan - did not rule out any options regarding Syria, but said he did not expect US troops would be sent on the ground. He added that the leaders in the region he has consulted with on the issue agree with him.
"As a general rule, I don't rule things out as commander-in-chief because circumstances change and you want to make sure that I always have the full power of the United States at our disposal to meet American national security interests," Obama said.
"Having said that, I do not foresee a scenario in which boots on the ground in Syria, American boots on the ground in Syria, would not only be good for America but also would be good for Syria."
Obama said it would be a "game changer" if strong evidence was found that the regime of Syrian President Bashar al-Assad had used chemical weapons, because "there is a possibility that it lands in the hands of organizations like Hezbollah."
He insisted the US was not standing by while it waits for evidence. "We're not waiting. We are working to apply every pressure point that we can in Syria," the US president said.
"If in fact there is the kind of systematic use of chemical weapons inside of Syria, we expect we are going to get additional further evidence and at that point we will absolutely present that to the international community," Obama said.
Obama told a news conference that the US is already putting pressure on the Syrian government, through options such as humanitarian aid to the opposition.
jr/hc (AP, AFP, Reuters)
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