On Monday, fighting between the two militant groups erupted in the Syrian town of al-Nairab. A number of ISIL militants were also captured during the fighting.

The so-called Islamic Front, which is the biggest militant alliance in Syria, had earlier announced that it would fight against the ISIL.

Earlier in the day, the al-Qaeda-linked militants killed at least 50 rival militants in attacks including car bombings and summary executions.

Monday was the third day of infighting, which began when militants of the so-called Free Syrian Army (FSA) attacked checkpoints and bases manned by the ISIL.

Previously, the clashes were mostly in the northern provinces of Aleppo and Idlib, but opposition sources say the fighting has now spread to the east.

Also on Monday, the FSA laid siege to the ISIL militants in the Syrian city of Raqqa.

Clashes between militants from FSA and ISIL erupted in Raqqa overnight and the fighting continued on Monday, said Rami Abdurrahman, the director of the so-called Syrian Observatory for Human Rights.

Syria has been gripped by deadly unrest since 2011. According to reports, the Western powers and their regional allies -- namely Qatar, Saudi Arabia and Turkey -- are supporting the militants operating inside Syria.

According to the United Nations, more than 100,000 people have been killed and millions displaced in the foreign-backed militancy.

The UN also says more than four million other Syrians will be forced out of their homes in 2014 by the escalating conflict in the country.

BA/BA