BEIRUT: Jihadist fighters seized on Wednesday parts of a large military airport in northwestern Syria after a weeks-long siege, said a monitoring group.

"Troops clashed with Al-Nusra Front and Ahrar al-Sham fighters inside the Taftanaz military airport, after rebels broke in and seized large swathes of its grounds," said the Britain-based Syrian Observatory for Human Rights.

The jihadists destroyed several helicopter gunships during their assault, said the Observatory, which relies on a network of doctors, lawyers and activists for its reporting.

Army tanks pounded the airport grounds and several nearby villages in a bid to root out the rebels, said the watchdog.

Without commenting on the rebels' progress, a military source told AFP that several air strikes were carried out in the area to try and force insurgents to withdraw from areas surrounding the airport.

Elsewhere in northern Syria, the Observatory reported fierce fighting near military airports at Minnigh, Kwiyres and Nayrab in Aleppo province.

All three have been besieged for weeks by rebels, most of them jihadists.

Al-Nusra, made up of bearded fighters with good combat experience and Islamist views, makes no secret of its desire to see Syria one day become an Islamic caliphate.

It is listed as a "terrorist" organisation by the United States.

Fighting raged across flashpoints in Syria hours after four children from the same family were among as many as 10 civilians killed in a pre-dawn air strike near the central city of Homs, the Observatory said.

The Observatory said the siblings were aged seven months, and 12, 14 and 16 years.

According to a preliminary toll compiled by the Observatory, at least 27 people were killed in violence across Syria on Wednesday, among them 22 civilians.

In all, more than 60,000 people have been killed since the revolt against President Bashar al-Assad's rule erupted in March 2011, according to the latest UN figures.