BEIRUT - An airstrike near the Syrian capital on Friday killed top rebel commander Zahran Allouch, the head of one of the most powerful Saudi-backed insurgent groups fighting against President Bashar al-Assad's government near the seat of his power Damascus, opposition activists said.

Allouch's death a month before expected peace talks between government and opposition representatives in Geneva is a blow to insurgents fighting to topple Assad and a boost to government forces who have been bolstered by the Russian military intervention in Syria in the last few months.

It was not immediately clear who was behind his death.

The Britain-based Syrian Observatory for Human Rights said an airstrike hit an Army of Islam meeting near the Damascus suburb of Otaya, killing several rebel commanders including Allouch. It said it was not clear whether it was a Russian or Syrian airstrike.

The Observatory said the warplanes struck a meeting during which Army of Islam commanders were preparing to launch an offensive against government forces and those of Lebanon's Hezbollah near Damascus.

The Local Coordination Committees earlier said that Allouch was killed along with his deputy and chief spokesman in an airstrike believed to be Russian in Otaya.

The Syrian military, in a statement published on the state-run SANA news agency, said later Friday that Allouch was killed in a Syrian army airstrike.

It said that the strike was carried out after a series of aerial reconnaissance operations against groupings of "terrorist" organizations and their headquarters in Eastern Ghouta. In addition to Allouch, it said the airstrike killed "a large number of commanders of Ahrar al-Sham and Faylaq al-Rahman."

It was not immediately clear how Allouch's killing would affect his group, which is entrenched in the eastern suburbs of Damascus. Several rebel group commanders have been killed in the past - including most of the command of the ultraconservative Ahrar al-Sham group in a mysterious bombing in northern Syria last year.

Allouch, who was in his mid-40s, was widely known to be supported by Saudi Arabia and Turkey. He was one of the most powerful rebel commanders with thousands of fighters controlling large parts of the eastern Damascus suburbs known as Eastern Ghouta and Douma. In addition to fighting government forces, the Army of Islam faction fought pitched battles against its rival, the Islamic State group near Damascus.

A former prisoner who was released in a general amnesty after the uprising against Assad began in March 2011, Allouch joined the armed opposition and formed the Army of Islam - which became one of the most organized rebel factions in Syria.

Critics accuse him of sectarian politics and brutal tactics similar to that of the Islamic State group.