Nusra Front fighters in Syria
Nusra Front fighters in SyriaReuters

Islamist rebels including Al Qaeda's Nusra Front have seized control of two key Syrian army bases in northwestern Idlib province, in a major blow to Assad forces Monday.

Nusra Front rebels were aided by Jund al-Aqsa and Ahrar al-Sham in taking the Wadi al-Deif base in a major assault launched on Sunday morning, according to the Syrian Observatory for Human Rights.

At least 31 soldiers and 12 rebels were killed in the fighting, which came just a day after rebels seized seven nearby checkpoints, along with the Hamidiya military base.

Several previous attempts to take Wadi al-Deif were repelled by pro-regime forces.

The latest development effectively puts Al Nusra and its allies in control of the majority of Idlib province, with regime forces largely confined the province's capital.

Significantly, it also follows Nusra's routing of the western-backed Syrian Revolutionary Front (SRF) in the area, highlighting the growing dominance of the Al Qaeda franchise in Syria's bloody civil war.

"The jihadists' advance has major symbolic importance, and it also shows the rebels that Al-Nusra Front really is in control of the area," said Observatory director Rami Abdel Rahman.

In its attack on Wadi al-Deif, "Al-Nusra Front used tanks and other heavy weapons that it captured last month from the Syrian Revolutionary Front", he told AFP.

While western-backed rebels still dominate in southern Syria, the north of the country has increasingly been taken over by radical elements, including the Nusra Front and ISIS.