Nusra Front fighters (file)
Nusra Front fighters (file)Reuters

 A rebel coalition including Al Qaeda's local affiliate seized the Syrian regime's largest remaining military base in northwest Idlib province on Tuesday, after an explosion and heavy clashes, a monitor said.  

"All regime forces have withdrawn from Al-Mastumah, the largest regime base in Idlib, leaving it completely in the hands of opposition fighters," Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, told AFP.  

The rebel alliance that seized the camp calls itself the "Army of Conquest" and includes Al Qaeda affiliate Al-Nusra Front and other Islamist factions.

"With the help of God, Al-Mastumah was completely liberated after Al-Nusra Front stormed it from the south," the affiliate wrote on its official Twitter account.  

The loss of Al-Mastumah is the latest setback in Idlib province for the regime, which lost control of the provincial capital in March and the regime stronghold of Jisr al-Shughur in April.

Regime forces withdrew to the town of Ariha further south, which, along with the Abu Duhur military airport and a few small government positions, make up the last remaining regime military presence in Idlib province.

A Syrian military source told AFP that clashes were ongoing in Al-Mastumah camp and the nearby town of the same name.

Syrian state television said the army was "taking defensive positions" outside of Ariha, implying that army units had withdrawn from Al-Mastumah itself.