A Syrian regime air strike on a field hospital in the northern province of Aleppo killed at least 11 people on Wednesday, the Syrian Observatory for Human Rights said.

"At least 11 people, including a doctor... were killed in an air strike on a field hospital in Al-Bab," the Britain-based monitoring group said.

On Monday, regime air strikes hit a school in the town, in northeast Aleppo province, which was being used as a base by the Islamic State of Iraq and the Levant -- an Al-Qaeda affiliate.

Elsewhere, jihadists killed at least 20 civilians in the central province of Homs on Tuesday, with members of the Qaeda-linked Al-Nusra Front among the assailants, said the Observatory.

Fighters from Al-Nusra and another rebel group attacked three Alawite villages near the city of Homs, said the group which gets its information from a network of activists, lawyers and medics.

"Fierce clashes broke out between rebels and army troops," Observatory director Rami Abdel Rahman told AFP.

The rebels entered the village of Maksar al-Hissan and killed 16 members of the Alawite sect, the religious community to which President Bashar al-Assad belongs.

They also killed four Bedouin residents of the village, the Observatory said.

Troops retook the village on Tuesday night, after clashes in which they lost two men and killed several members of Al-Nusra.

The region, which is mostly home to Alawites and Bedouin communities, has been largely free of fighting during the past year.

Government forces control most of the central province of Homs, parts of which have suffered some of the fiercest fighting and destruction in Syria's 30-month war.