Israel has confirmed it has conducted an air strike against Syria.
News of the air strike initially came from sources in the United States, although neither the US nor Israel would say for sure it had happened.
Now, Israeli officials, speaking anonymously, say one of its aircraft targetted a shipment of missiles in Syria believed to be going to Hezbollah guerrillas in neighbouring Lebanon.
Initial reports said the aircraft did not actually enter Syrian airspace.
In January, Israel bombed a convoy inside Syria that was thought to be carrying anti-aircraft missiles to Hezbollah. The Israeli embassy in Washington says Israel is determined to prevent the transfer of weapons to militant groups, particularly Hezbollah in Lebanon.
Obama can't foresee sending troops
Meanwhile President Barack Obama has said he does not foresee a scenario that would require sending US troops to Syria.
He reaffirmed that clear evidence that the Syrian government had used chemical weapons would be a "game-changer", but that any response would not be rushed.
Mr Obama told reporters in Costa Rica on Friday that as commander-in-chief he could rule nothing out "because circumstances change", the BBC reports.
But he added he did not foresee a scenario in which "American boots on the ground in Syria" would be good for either America or Syria.