In this Thursday, Feb. 11, 2016 photo, civilians carry supplies in Aleppo, Syria.

The “vast majority” of armed groups eligible to take part in a cessation of hostilities in Syria have signaled that they will do so, a source close to the peace talks told Reuters on Friday.

It was unclear if any groups had refused to sign up. Under the terms of the deal, armed groups had to confirm their commitment to the United States or Russia no later than 1200 Damascus time (1000 GMT).

The cessation of hostilities will begin at midnight.

Under threat

But hours before the agreement was set to take place, Syria’s branch of al Qaeda, one of its most powerful Islamist rebel groups, called for an escalation in fighting against the government and its allies.

Al-Nusra Front’s leader, Abu Mohamad al-Golani, said in an audio message on Orient News TV on Friday that insurgents should “strengthen your resolve and intensify your strikes, and do not let their planes and great numbers (of troops) scare you.”

Unlike ISIS, which controls defined areas of territory in central and eastern Syria, the Nusra Front is widely dispersed in opposition-held areas in the west, and any escalation would add to the risks of the truce collapsing.

Nusra is bigger than nearly all the factions taking part in the cessation, with fighters across western Syria.

The truce does not apply to militant groups such as ISIS and the al Qaeda-linked Nusra Front, and the Damascus government and its Russian allies say they will not halt combat against those militants. Other rebels seen as moderates by the West say they fear this will be used to justify attacks on them.

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