Air strikes destroyed rebel-held eastern Aleppo's biggest hospital Monday as Syria's regime pressed its Russian-backed offensive to retake the entire city and the United States targeted a top Al-Qaeda member.

The M10 hospital was "completely destroyed" following multiple strikes over the past week, the medical organisation that supports it said.

"The hospital is now not usable at all," said Adham Sahloul of the Syrian American Medical Society. "It is not salvageable, per reports from the staff and doctors there".

He said three maintenance workers were killed in the air strikes.

The Syrian Observatory for Human Rights monitoring group confirmed that the hospital was destroyed after "being directly targeted by air raids".

Also Monday, a US air strike targeted a top Al-Qaeda member, the Pentagon said, amid reports that a senior leader of the extremist group had been killed near Idlib.

"We can confirm that we targeted a prominent Al-Qaeda member in Syria, and we are assessing the results of the operation at this time," Pentagon spokesman Navy Captain Jeff Davis said.

"This is a prominent Al-Qaeda leader."

Word of the strike came as regional news reports and social media postings said Ahmed Salama Mabrouk, an Egyptian also known by the nom de guerre Abu Faraj, had been killed.

Mabrouk, born in 1956 in Egypt's Giza province, is known as a veteran Al-Qaeda leader and a commander of the Fateh al-Sham Front, which changed its name from Al-Nusra Front following a break with Al-Qaeda.

- International outrage -

Strikes against civilian infrastructure in the Syrian regime's offensive have sparked international outrage and accusations of war crimes.

Moscow on Monday denied it was bombing hospitals, saying its bombing campaign was "highly effective" and had stopped jihadists taking over Syria.

"Accusations that Russia is allegedly bombing medical facilities, hospitals, schools are all baseless," Deputy foreign minister Gennady Gatilov said in comments reported by Russian media.

A short-lived truce brokered by Moscow and Washington earlier this month could have led the two countries to coordinate strikes against jihadists, but the deal quickly collapsed.

The UN Security Council was on Monday considering a draft UN resolution imposing a ceasefire in Aleppo and putting an end to all military flights over the battered city.

The French-drafted text obtained by AFP was circulated to the Security Council at the weekend and a vote could take place this week, diplomats said.

Meanwhile, air strikes on a besieged rebel-held town east of Damascus on Monday sparked fears that it could face a fate similar to that of Aleppo.

More than a dozen raids and several mortar rounds pounded Douma in the Eastern Ghouta opposition stronghold, said the Britain-based Observatory.

The bombardment is part of a five-month offensive by government forces that has "chipped away at opposition territory" there, Observatory head Rami Abdel Rahman told AFP.

- Suicide blasts -

Backed by allied militia, Syria's army has advanced to just three kilometres (two miles) east of Douma, the largest rebel-controlled town in the area and the focus of the latest military push, he said.

AFP's correspondent in Douma said he counted at least 10 strikes on Monday morning alone.

As Syrian forces pressed their advances in Aleppo and Douma, at least two people were killed in rare suicide blasts, claimed by the Islamic State jihadist group, in the central regime-held city of Hama.

State news agency SANA, citing local police, said two "terrorists" detonated their explosive belts near the central Assi Square some 15 minutes apart.

The attack killed two people and wounded 12, Hama governor Ghassan Khalaf told state television.

IS holds some territory in northeastern swathes of Hama province, but it is the first time they have claimed an attack in the city itself, which has remained relatively insulated from Syria's five-year war.

Elsewhere, at least 21 Turkish-backed Syrian rebels fighting the Islamic State group were killed on Sunday by landmines laid by the jihadist group, the Observatory said.

The toll was the highest loss of life for forces involved in the Turkish-led operation in northern Syria since it began in late August, it said.

It did not mention any Turkish casualties.

Turkey began its unprecedented operation inside Syria, dubbed Operation Euphrates Shield, on August 24.

The rebels were trying to secure the village of Turkman Barah, near the flashpoint IS-held town of Dabiq in Aleppo province.

Ankara says it is targeting IS but also Kurdish fighters from the People's Protection Units (YPG), which Turkey considers to be a "terrorist" group.

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