Syria's Al-Qaeda affiliate on Sunday set its conditions to stop battling the rival Islamic State of Iraq and the Levant, despite an order by the Al-Qaeda chief to quit fighting.
Al-Nusra Front and ISIL have in recent months fought intense, bloody battles against each other, particularly in eastern Syria on the border with Iraq.
"We will follow the orders of... Ayman al-Zawahiri... to stop any attack from our side against ISIL, while continuing to respond whenever they attack Muslims and all that is sacred to them," Al-Nusra said in a statement.
"As soon as ISIL announces the end of its attacks on Muslims, we will spontaneously stop firing," said the jihadist group, adding it had only fought ISIL in areas "where it was on the attack".
While rebels fighting to topple President Bashar al-Assad initially welcomed both Al-Nusra Front and later ISIL in the Syrian war, widespread opposition to ISIL later emerged over its quest for dominance in opposition-held areas.
Rebels including Islamists launched a massive offensive against ISIL on January 3, and Al-Nusra Front joined the fight against the group later on.
As far back as last June, Zawahiri weighed in on ISIL's involvement in Syria, designating Al-Nusra as responsible for operations there and ordering ISIL chief Abu Bakr al-Baghdadi to restrict the group's activities to its home base in Iraq.