Israeli air strikes destroyed the Iranian embassy's consular annex in Syria on Monday, killing and wounding everyone inside, Damascus said as Iranian state TV reported a Revolutionary Guards commander among the dead.
Britain-based war monitoring group the Syrian Observatory for Human Rights said 11 people, including several Guards members, were killed when "Israeli missiles destroyed the building of an annex to the Iranian embassy".
Iran's ambassador to Syria, Hossein Akbari, giving a lower death toll, told Iranian state TV that "at least five people were killed in the attack which was carried out by F35 fighter jets".
Israel did not immediately comment on the deadly attack in Damascus which comes at a time of soaring tensions over its deadly war in the Gaza Strip, and intensifying violence between Israel and Iran's allies.
AFP reporters saw the annex building had caved in, and emergency services were rushing to search for victims under the rubble as sirens wailed in the upscale Damascus district of Mazzeh.
Security sources shielded the site where earth-moving equipment was brought in to clear the debris and remove charred vehicles from the road outside, watched by a crowd of onlookers.
Syria's defence ministry said "the attack destroyed the entire building, killing and injuring everyone inside, and work is underway to recover the bodies and rescue the wounded from under the rubble".
Iranian state TV said among those killed was a senior commander of the Islamic Revolutionary Guard Corps' foreign operations arm, the Quds Force, Brigadier General Mohammad Reza Zahedi.
The Observatory said it had "confirmed the killing of a high-ranking leader who served as the leader of the Quds Force for Syria and Lebanon, two Iranian advisors, and five members of the Iranian Revolutionary Guard".
The Damascus strikes were the fifth in eight days to hit Syria, whose President Bashar al-Assad is supported by Iran, Israel's long-time arch foe in the region.
Syria's state news agency SANA had earlier reported that "our air defence systems confronted enemy targets in the vicinity of Damascus".
Iran's ambassador, Akbari, said that "the Israeli attack on the Iranian consulate shows the reality of the Zionist entity which recognises no international laws and does all that is inhumane to achieve its goals".
Iranian Foreign Minister Hossein Amir-Abdollahian called for a "serious response by the international community".
Syrian Foreign Minister Faisal Mekdad also denounced the attack after visiting the site.
"We strongly condemn this heinous terrorist attack that targeted the Iranian consulate building in Damascus killing a number of innocent people," Mekdad said in a statement carried by SANA.
Israel's military onslaught in Gaza has killed 32,845 Palestinians as of Monday, and has devastated the coastal territory. The military campaign has also seen Israel and the Lebanese Hezbollah group exchange near daily cross-border fire.
Israel has also struck targets in Syria, mostly army positions as well as those of Iran-backed combatants.
The Damascus strike came three days after the Observatory reported Israeli strikes that had killed 53 people in Syria, including 38 soldiers and seven members of Hezbollah.
It was the highest Syrian army toll in Israeli strikes since the Israel's war in Gaza war began, said the monitor.
"Syria and Lebanon have become one extended battleground from the Israeli perspective," Riad Kahwaji, head of the Institute for Near East and Gulf Military Analysis, told AFP after the Friday strikes.