Two people were killed and several wounded on Monday in what Iranian and Syrian media said was an Israeli attack on the outskirts of the Syrian capital, with Iran's ambassador to Damascus denying reports the location was an Iranian military post.
An Israeli military spokesperson declined to comment on the explosions.
Iranian state media reported the two deaths but did not identify the victims. Tasnim news agency said Israel "attacked an Iranian military advisory centre" in Syria, but Iran's envoy to Syria, Hossein Akbari, denied the details on the target and said the casualties were not Iranian.
Syrian state media, citing a military source, said Israel had launched an air assault on several locations south of Damascus. It said the attack left both dead and wounded but did not specify any numbers.
In a first version of the story on its site, Syrian news agency SANA said the dead included an unspecified number of "Iranian advisers" - a rare admission of Iranian casualties by Damascus - but the site was updated to remove the reference.
The attack comes a day after three U.S. troops were killed in a drone attack on a military outpost in Jordan, the first time American troops have been killed under fire since the Israel-Gaza war erupted in October.
Since then, U.S. forces have come under attack more than 150 times by Iran-backed groups in Iraq and Syria, causing at least 70 casualties prior to Sunday's attack, most of them traumatic brain injuries.
On Monday, a shell landed on a military base used by the U.S.-led coalition in eastern Syria, without causing any casualties, according to a security source in the area.
The deaths on Sunday mark a major escalation in the violence already engulfing the Middle East, with Israel striking Lebanon and the United States bombing Iraq and Yemen.
U.S. President Joe Biden said the U.S. would respond. His political opponents seized on the incident to criticise him, saying the deaths were evidence he had failed to confront Tehran and urging military action against Iran.
An Israeli strike earlier this month killed an intelligence chief in the Iranian Guards' Quds Force, along with four others.
