Mohammed Golani, the chief of Al-Qaeda in Syria - otherwise known as the Nusra Front - has slammed ISIS in the second part of a TV interview series aired on Wednesday.
"They announced a caliphate, but the scholars rejected it as illegitimate. It is not based on Islamic law," Golani said on Qatari-owned Al-Jazeera news channel.
The fierce fighting between two groups heated up after ISIS proclaimed itself to be a state last summer.
Golani said that ISIS murdered 700 members of Nusra in a single battle, including women and children.
“There is no solution between us and them in the meantime, or in the foreseeable future,” said Goloni.
“We hope they repent to God and return to their senses ... if not, then there is nothing but fighting between us.”
The rivalry began between two groups after a split occurred in 2013 is largely due to a power struggle between Abu Bakr al-Baghdadi and Al-Qaeda’s leadership.
Nusra chief Golani dodged a question about whether a split is possible between his organisation and Al-Qaeda.
“The issue is not about leaving Al-Qaeda. It is about who rises up against hegemony,” said Golani.
He also said that every three out of ten of its fighters are foreigners, including a “small number” of Americans.
Nusra was part of a larger opposition coalition that recently seized Idlib, a northern province in Syria.
In the Al Jazeera interview Golani also once again rejected political solutions to Syria’s war which has so far claimed more than 220,000 lives.
"We are only here to accomplish one mission, to fight the [Bassar Assad] regime and its agents on the ground, including Hezbollah and others," he said.