Activists said on Monday that ISIL forces had pulled back to the eastern provinces of Raqqa and Hassaka after days of infighting with al-Nusra Front.
"The ISIL militants have almost completely withdrawn from Deir al-Zour. The fighters are moving to Hassaka and Raqqa (provinces)," said a source from the Nusra Front, who asked not to be named. Raqqa remains the stronghold of ISIL.
ISIL maintains a permanent base in Raqqa.
Pro-ISIL activists on Twitter said the group had withdrawn from Deir al-Zour to prevent further bloodshed.
ISIL, which has attracted many foreign extremist militants into its ranks, is a powerful militant force fighting at the side of opposition in Syria.
ISIL is the rebranding of al-Qaeda's affiliate in neighboring Iraq, but it defied the central leadership's requests to limit itself to fighting there instead of Syria. Al-Qaeda's central leadership formally announced a split with ISIL earlier in February.
The so-called Syrian Observatory for Human Rights, a pro-opposition monitoring group, said Deir al-Zour was now in the hands of Nusra Front which is al-Qaeda's main force on the ground in the country.
NTJ/SHI