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CAIRO, Egypt - Rebel commanders in Syria issued a 48-hour ultimatum to al Qaeda-affiliated fighters Tuesday, ordering them to surrender or face “a massacre.”

The resurgent Free Syrian Army is taking back areas previously lost to a splinter group known as the Islamic State in Iraq and the Levant (ISIL) – a faction that has turned the deadly civil war into a complex battle in which opponents of President Bashar Assad’s regime are also fighting each other.

More than 274 people have been killed in the rebel-on-rebel clashes since Friday, according to the Syrian Observatory for Human Rights, an opposition monitoring group.

FSA commander Gen. Mna’ Rihal told NBC News that ISIL must end its campaign and abandon its attempts to create “religious division” between anti-Assad forces.

“We are showing them goodwill from a strong position, and giving them the ultimatum to prevent a massacre,” he said by telephone from the northern city of Idlib. “We are trying to spare bloodshed."

He said ISIL had been “expelled” from its previously-held areas in the north and that 10 of its leaders in Idlib and the nearby city of Aleppo had been arrested.

In addition, he said, "300 [fighters] have been captured. Some others blew themselves up with explosive belts."

“We have given them a 48-hour ultimatum to surrender and give up their weapons.  The ultimatum will end on Friday morning.  They must drop their weapons and surrender…if they do, they will be safe.

“They came from far away to kill our women.  As long as they join ranks and cooperate and we have one aim to get Bashar al Assad out, they can join us.”

Asked how the local population felt about the resurgence of the FSA against ISIL, Rihal said: “Their feeling is as if they had ousted Bashar Assad.”

It is almost impossible to verify claims made by any of the sides in Syria’s deadly conflict.

As Rihal spoke, the head of another rebel group, the Nusra Front, called for a ceasefire between opposition factions, Reuters reported.

An audio recording from Mohammed al-Golani laid much of the blame for infighting on ISIL.

While both the Nusra Front and ISIL are tied to al Qaeda, the former has been cooperating more closely with other rebel groups.

"Many rebel units have committed transgressions, just as the mistaken policies followed by played a prominent role in fuelling the conflict," Golani said, according to Reuters. "In addition to this, there has been no agreement on legal solutions agreed upon by all major units."

Golani urged rebels not to become divided between foreign and local fighters, arguing that all were needed to launch jihad, or holy war, in the country.

NBC News' Alastair Jamieson and Reuters contributed to this report.