The United States announced on Saturday its support for Israel's airstrikes on Iranian positions inside Syria, blaming Iran for escalating violence.
Israel's military launched attacks on a dozen targets after an Israeli jet crashed under fire from Syria's air defences. The last time an Israeli jet was shot down under enemy fire was in the early 1980s, according to the New York Times.
The Israeli raids came after it intercepted an Iranian drone allegedly entering its airspace.
"The United States is deeply concerned about today's escalation of violence over Israel's border and strongly supports Israel's sovereign right to defend itself," said Heather Nauert, US State Department spokeswoman.
Saturday's incidents mark the most serious confrontation between Israel and Iran since the Syrian war began in 2011. Prime Minister Binyamin Netanyahu has vowed to prevent Iran from consolidating its power in Syria.
"The US continues to push back on the totality of Iran's malign activities in the region and calls for an end to Iranian behaviour that threatens peace and stability," added Nauert.
The US has been a staunch ally of Israel for decades.