Fighters from the Islamic State of Iraq and the Levant (ISIL) have withdrawn from Syria's oil-rich eastern province of Deir al-Zor, activists and rebels said, after days of heavy fighting with rivals.

"The ISIL fighters have almost completely withdrawn from Deir al-Zor. The fighters are moving to Hassaka and Raqqa (provinces)," a source from the Al-Qaeda-affiliated Jabhat Nusra told the Reuters news agency on Monday.

Raqqa remains the stronghold of ISIL, which has been criticised for introducing hardline rules against civilians and executing dissenters. Last week Al-Qaeda disavowed all links with ISIL after it killed rival rebel leaders in a number of car bombings.

Rebel groups, including Jabhat al-Nusra, have been battling ISIL for control of towns and oilfields in the area, sparking a spate of car bombs in the province.

Pro-ISIL activists on Twitter said the group had withdrawn from Deir al-Zor to prevent further bloodshed.

Several rebel groups launched a campaign last month to try to push ISIL, their former allies, out of opposition-held regions in northern and eastern Syria.

The loss of Deir al-Zor province could be a serious setback for ISIL, as it holds oil reserves and is a key conduit for the group to receive weapons and fighters from neighbouring Iraq.

Widespread violence

Barrel bomb attack in Aleppo

In other fighting, government forces were reported to have killed 15 people in another round of barrel bombings.

Civilians in the city have suffered days of similar attacks, with hundreds reported dead.

Barrel bombs - containers laden with explosives and launched from helicopters - have been condemned by international groups as indiscriminate

Opposition fighters meanwhile killed at least 21 civilians and 20 pro-regime fighters in an Alawite village in Syria's Hama province, the British-based Syrian Observatory for Human Rights reported.

The group said fighters from groups including Jund al-Aqsa were behind the deaths in Maan village, in central Syria, on Sunday.

Observatory director Rami Abdel Rahman said there were no immediate details on how the civilians had been killed, but added that at least 10 of them appeared to be from a single family.

The group said at least 20 members of the National Defence Forces, a pro-regime group, had been killed in the attack.

Source: Agencies