Activists say militants led by al-Qaida's branch in Syria are advancing in the northwestern province of Idlib after capturing a government stronghold.

The Syrian Observatory for Human Rights and the Local Coordination Committees said Friday that the so-called Fatah Army has captured several villages near the town of Ariha, which the insurgents seized the day before. Ariha had been one of the last major government strongholds in Idlib.

The Fatah Army includes seven Syrian armed factions and is led by al-Qaida's Nusra Front. Turkey and Saudi Arabia support the coalition.

The Observatory, which is based in Britain but relies on activists inside Syria, said militants killed 13 troops and pro-government gunmen after capturing them alive in Ariha. It says 18 others were killed as they fled the town.