Activists say al-Qaida's Syrian branch and other insurgents have captured a strategic overlook from government forces south of Aleppo after weeks of government air raids, in fighting that could unravel a month-old cease-fire.

The Britain-based Syrian Observatory for Human Rights says the al-Qaida-affiliated Nusra Front, along with other jihadis as well as more moderate factions, captured the village of Tel el-Ais early Saturday.

The village overlooks a vital highway connecting Aleppo with the capital, Damascus.

The Nusra Front boasted of its offensive on social media, posting videos showing mortars and tanks firing on what is said to be government positions. Syria's state news agency acknowledged fierce clashes in the area.

Both the Nusra Front and the Islamic State group are excluded from the cease-fire that began in late February.