A rocket attack in Damascus on Sunday that Syria blamed on Israel hit an installation where Iranian officials were meeting to advance programmes to develop drone or missile capabilities of Tehran's allies in Syria, sources told Reuters.

Iran has been a major backer of President Bashar al-Assad during Syria's nearly 12-year conflict. Its support for Damascus and the Lebanese group Hezbollah has drawn regular Israeli air strikes meant to curb Tehran's extraterritorial military power.

A source close to the Syrian government with knowledge of Sunday's strike and its target said it hit a gathering of Syrian and Iranian technical experts in drone manufacturing, though he said no top-level Iranian was killed.

"The strike hit the centre where they were meeting as well as an apartment in a residential building. One Syrian engineer and one Iranian official - not high-ranking - were killed," the source told Reuters.

This rocket strike, along with others that Israel says target infrastructure of Syria's military and its allies, reflect an escalation of what has been a low-intensity conflict aimed at slowing down Iran's growing entrenchment in Syria, according to Israeli military experts.

Syrian state media said at the time that Israel had carried out air strikes shortly after midnight on Sunday against several areas of the Syrian capital, causing five deaths and 15 injuries including civilians.

An Israeli military official declined to confirm or deny that Israel was behind the attack, but said some of the casualties were caused by errant Syrian anti-aircraft fire.

The United States and Israel have been increasingly concerned about Iran’s drone manufacturing, and the possibility it would pass on those capabilities to regional proxies such as the heavily armed Hezbollah.

Last week U.S. forces shot down what they said was an Iranian-made drone flying over a base hosting U.S. personnel in northeastern Syria.