The Guards vowed to respond, saying the “criminal attack” on the outskirts of Damascus at dawn would not go “unanswered”, the semi-official Iranian news outlet Tasnim reported.

The air strike was the sixth attack by Israel in Syria this month, according to the Syrian Observatory for Human Rights.

Israel has for years carried out attacks against what it has described as Iran-linked targets in Syria, where Tehran’s influence has grown since it began supporting President Bashar al-Assad in the civil war that began in 2011.

Iran says its officers serve in an advisory role in Syria at the invitation of Damascus. Dozens of IRGC members including senior officers have been killed in Syria during the war.

Syrian state media said that Israel had attacked just after midnight, firing missiles that hit a site in the Damascus countryside. Syrian air defences had shot down a number of missiles, it said, without mentioning any casualties.

Iranian-backed groups, including Lebanon’s heavily armed Hezbollah, and Iraqi paramilitary groups have positions around the capital and in Syria’s north, east and south.

“This is a very dangerous stage, the risks are very high and we should expect more to come,” said Hamidreza Azizi, a visiting fellow at the German Institute for International and Security Affairs (SWP) in Berlin.

“The risk of escalation between Iran and Israel in Syria is higher than any time in the past few months, even possibly years,” he said.

The violence underlined the possibility of further tensions in Syria even as some of the Middle Eastern states that have vied for influence there move to improve ties – notably Riyadh and Tehran – and as several Arab countries normalise ties with Assad.

After 12 years of war, Syria remains partitioned with several foreign armies on the ground, including U.S. troops.

Last week, Iran-backed groups launched armed drones at a base hosting U.S. forces in the northeast, killing one American contractor and wounding another, as well as several troops, the Pentagon said.

The U.S. responded with air strikes on installations in eastern Syria that it said were affiliated with the IRGC.

The Pentagon said on Thursday that six U.S. troops suffered traumatic brain injuries during the tit-for-tat exchanges last week.

Friday’s attack followed a strike on Thursday that wounded two soldiers, according to Syrian state media. A source with Syria’s opposition factions said it hit a car carrying pro-Iran personnel near a Syrian security building.

On March 22, an Israeli strike near the airport at the northern city of Aleppo briefly put it out of service. Regional intelligence sources said the attack hit an Iranian arms depot.

Iran’s foreign ministry strongly condemned the two attacks on Syria this week.

The Syrian foreign ministry also condemned Friday’s attack and said Syria stood ready to confront any further attacks.