A rocket attack in Damascus on Sunday that Syria blamed on Israel hit an installation where Iranian officials were meeting to advance programs 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 center 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 the 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 US forces shot down what they said was an Iranian-made drone flying over a base hosting US personnel in northeastern Syria.
A second source, who spoke to Syrian security personnel briefed on the matter, said Iranians were attending the meeting of technical experts in an Iranian military installation in the basement of a residential building inside a security compound.
He said one of those killed was a Syrian army civil engineer who worked at Syria's Scientific Studies and Research Centre, which Western countries say is a military institution that has produced missiles and chemical weapons. Damascus denies this.
A regional security source said one Revolutionary Guards engineer involved in Iran’s missile program was seriously injured and transferred to a hospital in Tehran, while two other mid-ranking Guards members at the meeting were unharmed.
Another source, a regional intelligence official familiar with the strike, said the target was part of a covert guided missile production program run by Iran's Islamic Revolutionary Guard Corps (IRGC).
A fifth, regional source with knowledge of the strike and its target, said officials from Iran and Hezbollah had been targeted. The Lebanese group, which fought a five-week war with Israel in 2006, has sent fighters to help Assad drive back rebels who once nearly encircled Damascus.
Revolutionary Guards logistics center hit?
On Sunday, the Iranian Foreign Ministry condemned what it described as attacks on "residential buildings in Damascus which killed and maimed innocent Syrian citizens." The ministry criticized what it called Western silence over Israeli violations of Syria's "territorial integrity."
It made no mention of Iranian casualties.
The Foreign Ministry and the Revolutionary Guards did not respond to Reuters requests for comment.
The targeted building was located in the Damascus neighborhood of Kafr Sousa, a heavily policed area where residents say several Iranian security agencies are located, along with an Iranian cultural center.
Two Western intelligence sources said at the time the target was a logistics center run by the Revolutionary Guards.
Hezbollah's top commander Imad Moughniyeh was killed in 2008 in a bombing in the same neighborhood. Israel denied Hezbollah accusations that it was behind the assassination.
Although officials rarely acknowledge responsibility for specific operations, Israel has been carrying out air strikes on suspected Iranian-sponsored weapons transfers and personnel deployments in Syria for almost a decade.
Israel has also in recent months intensified strikes on Syrian airports and air bases to disrupt Iran's increasing use of aerial supply lines to deliver arms to allies in Syria and Lebanon, including Hezbollah.
Iran's proxy militias, led by Hezbollah, now hold sway in large areas of eastern, southern and northern Syria and in several suburbs around the capital.
Assad has never publicly acknowledged that Iranian forces have operated on his behalf in Syria's civil war, saying Tehran has only military advisers on the ground.