Syria's Islamic Front, the country's biggest rebel alliance, issued Sunday a strong warning to jihadists, three days after a new front made up of local insurgents emerged against them.
"We fight against whoever attacks us and whoever pushes us to battle, whether they are Syrian or foreign," said the Front, an alliance that groups tens of thousands of rebels seeking to topple President Bashar al-Assad.
Since Friday, along with the Syrian Revolutionaries Front and the nascent Army of Mujahedeen, the Front has been engaged in fierce fighting with the jihadist Islamic State of Iraq and the Levant (ISIL).
The focus of combat has been in opposition areas in Aleppo and Idlib provinces, but spread to Hama and Raqa provinces on Sunday.
Scores of fighters have been killed on both sides in battle as well as in ambushes, car bomb attacks and summary executions by ISIL.
ISIL has been accused of horrific abuses in areas where it operates, and also of seeking hegemony by taking key roads and checkpoints from its rivals.
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Some Assad opponents have even accused it of serving regime interests.
"In our charter... we said we are grateful and thankful to the foreigners who came to help us" in the war against Assad's troops, the Islamic Front said in Sunday's statement.
But "we will not accept any group that claims to be a state."
Analysts say a key complaint against ISIL among rebels, including Islamists, is that its jihadists refuse to operate within the broader opposition dynamic.
Instead, it commands its own institutions and rejects cooperation with other rebel groups.
The Islamic Front's statement comes a day after ISIL distributed an audio statement warning rebels to stop pressuring it, or that it would withdraw from the front lines in Aleppo city and let in Assad's forces.
ISIL also accused its rivals of waging a "media war" against it, and of "stabbing (it) in the back."