Al-Qaeda-linked Islamic State of Iraq and the Levant (ISIL) vowed to "crush the rebel groups that have been fighting it across northern and central Syria" in a surprise campaign that began late last week.
An audio recording issued by the group also lashed out at the opposition Coalition, saying its members were now "legitimate targets".
Abu Mohammad al-Adnani called on ISIL fighters in Syria to "crush Opposition militants totally and kill the conspiracy at birth”, warning them that "none of you will remain, and we will make of you an example to all those who think of following the same path".
Golani threatens "the foreigners and supporters will pay the price for losing this great jihadist fighting arena" msaid in the recording uploaded to a militant website, referring to non-Syrians and Syrians.
The defiant stance came after the leader of another Al-Qaeda-linked group, al-Nusra Front, urged an end to the clashes in opposition-held territories, warning it threatened to reverse gains made against Syrian army.
More than 300 people have been reported killed since the clashes erupted Friday, with the figure including several dozen people whose bodies were discovered after they had been executed by ISIL militants.
The clashes began in Aleppo and Idlib provinces and has spread to Hama, Homs, and the province of Raqqa.
Al-Nusra Front and its rival ISIL are ideologically similar: Both are extreme Islamist groups, loyal to Al-Qaeda. But al-Nusra Front is dominated by Syrian fighters, , while ISIL has focused on building Islamic rule.