BEIRUT: A militant group has executed 41 fighters from Al-Qaeda's former Syria affiliate and allied factions in infighting between the extremists in Syria's Idlib province, a monitor said on Friday.

The Syrian Observatory for Human Rights said the Jund al-Aqsa group had captured the fighters and shot them to death in the town of Khan Sheikhun on Monday.

The deaths were only confirmed on Friday amid fierce fighting between the militant factions, said the Britain-based monitoring group.

Jund al-Aqsa has been locked in clashes with former Al-Qaeda affiliate Fateh al-Sham since Monday, after tensions erupted between them over influence in the rebel-held province of Idlib.

Fateh al-Sham is fighting alongside several allied groups in a coalition dubbed Tahrir al-Sham, and the clashes have spread beyond Idlib to neighbouring Hama province.

The Observatory said the clashes had killed 125 fighters from both sides, including the 41 executed by Jund al-Aqsa.

Jund al-Aqsa is reviled by most rebels in the region, and is designed a "terrorist group" by Washington.

Despite that, in October Fateh al-Sham announced it had taken Jund al-Aqsa under its wing, although clashes between the two groups erupted shortly afterwards.

In January, Fateh al-Sham also battled other rebel groups in Idlib during 10 days of clashes that killed dozens of fighters.

The fighting reflects the increasingly strained relations between different factions in Idlib province that once fought alongside each other against President Bashar al-Assad's forces.

Idlib province is held almost entirely by opposition factions, and was captured by an alliance of fighters dubbed the Army of Conquest, led by Fateh al-Sham.

More than 310,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests.

The war has become a complex multi-front conflict, drawing in militant groups and international armies.