Ambulances and fire trucks gathered around the site of the strike, which had been cordoned off, a Reuters journalist at the scene said. Rescue operations for people stuck under the rubble continued through the day. A crane was in place to hoist concrete slabs off the wreckage.
A security source in a network of groups close to Syria's government and its ally Iran told Reuters the multi-storey building was used by Iranian advisers supporting President Bashar al-Assad's government. It was completely flattened by "precision-targeted Israeli missiles", the source said.
The Guards said an unspecified number of members of the Syrian military were killed, along with the five Iranians, whom it identified without giving their ranks. The security source said one of the slain Iranians ran the elite force's information unit.
There was no comment from Israel, which has long pursued a bombing campaign against Iran's military and security presence in Syria but typically does not discuss such attacks publicly.
It has killed Iranian Guards in several such strikes in a stepped-up campaign in the wake of the October 7 attack on Israel by militants of the Iranian-backed Palestinian Islamist group Hamas from Gaza.
The strike was a "desperate attempt to spread instability in region", said Iran's Foreign Ministry spokesperson Nasser Kanaani in remarks reported by state media.Â
"Iran...reserves its right to respond to the organised terrorism of the fake Zionist regime at the appropriate time and place."
Syrian state media reported an Israeli "aerial attack" on a building in the Mazzeh neighbourhood of Damascus and said Syrian air defences had shot down a number of missiles.
Essam Al-Amin, head of the Al-Mowasat Hospital in Damascus, told Reuters that his hospital had received one dead body and three wounded people, including a woman, following Saturday's attack.
Palestinian Islamic Jihad, an Iranian-backed Palestinian faction present in Syria and Lebanon, condemned the air strike but told Reuters that none of its members were wounded, dismissing reports that some were at the bombed-out building.
Iran and its military allies in Syria have entrenched themselves in wide areas of eastern, southern and northern Syria and in several suburbs around the capital.
In December, an Israeli air strike killed two Guards members, and another near Damascus on December 25 killed a senior adviser to the Guards who was overseeing military coordination between Syria and Iran.
Israel responded to the Hamas assault on southern Israel on Oct. 7 by unleashing a devastating air and ground war in Gaza with the aim of eradicating its ruling Islamist group. The conflict has reverberated across the Middle East with violence surging in Syria, Lebanon, northern Iraq and in the Red Sea.
In Lebanon, the Iranian-backed Hezbollah as well as local wings of Palestinian militant groups have fired rockets across the border at Israel in solidarity with Palestinians in Gaza.
On Saturday, an Israeli strike in south Lebanon killed two members of Hamas as they were travelling in their car, three security sources told Reuters.
