"Eleven people including seven civilians" and two Hezbollah fighters were killed in "Israeli bombardment" of a building in the Hamra neighbourhood of Homs, said the Syrian Observatory for Human Rights, updating an earlier toll of 10 dead.

The strikes completely levelled the building in one of the city's most affluent districts, and also hit other targets linked to Iran-backed groups, added the Observatory, which relies on network of sources inside Syria.

Four students and a woman and her son were among the dead along with an unidentified civilian, the Observatory said, while a Syrian working with Lebanon's Hezbollah group and an unidentified pro-Iran fighter were also killed.

A source close to Hezbollah confirmed to AFP that two of the Iran-backed militant group's fighters were among the dead.

The Syrian defence ministry said that "the Israeli enemy launched air strikes against a number of sites in Homs and its countryside... killing and wounding a number of civilians," without providing precise casualty figures.

State television aired footage of rescue teams searching the rubble of a collapsed building for survivors.

Israel has launched hundreds of air strikes on Syria since civil war broke out in the country in 2011. But it has stepped up its campaign against Iran-backed forces in its northern neighbour since its war with Hamas in Gaza began on October 7.

Israel rarely comments on individual strikes in Syria but has said repeatedly that it will not allow Iran to expand its presence.

Last week, the United States carried out air strikes on Iran-backed groups in Syria and Iraq, killing 45 people in retaliation for a drone attack that killed three US soldiers in Jordan.

On Wednesday, a drone strike hit a vehicle in the Iraqi capital Baghdad, killing two commanders of a pro-Iran group, a security source and a group member said, as regional tensions soar.