Syrian rebels, including the main Islamist factions, said on Monday the creation of a caliphate by the Islamic State (IS) was "null and void".
"We see that the announcement by the rejectionists of a caliphate is null and void, legally and logically," the groups said in a statement, using a pejorative term to refer to the extremist Islamic State.
Among the signatories was the Islamic Front, Syria's biggest rebel coalition, and Majlis Shura Mujahideen al-Sharqiya, an alliance that includes the Al-Qaeda affiliate Al-Nusra Front.
The statement, signed by the religious bodies of each rebel group, went on to say that the Islamic State's announcement "changes nothing in terms of how we perceive them, or how they we will deal with them".
The signatories of the statement have all been at war with IS - previously known as the Islamic State of Iraq and Syria - since January.
Syria's rebels initially welcomed IS among their ranks in their bid to oust President Bashar al-Assad, but they turned against the jihadist group because of its systematic abuses and its quest for hegemony.
The statement comes a day after the ruthless Islamic State declared a "caliphate" straddling Iraq and Syria, declaring its chief Abu Bakr al-Baghdadi "the caliph" and "leader for Muslims everywhere".