A spokesman for the Syrian Islamist militia Jabhat Fateh al-Sham, formerly called the Nusra Front, criticized a nationwide Turkish- and Russian-backed ceasefire in Syria on Friday, saying the political solution under this agreement would "reproduce the criminal regime".

The group, which changed its name and announced in July that it was severing ties with al Qaeda, condemned the deal for not mentioning President Bashar al-Assad's fate.

"The solution is to topple the criminal regime militarily," the group's spokesman said in a statement.

The conflict pits Assad, helped by Russian air power and Iranian-backed Shi'ite Muslim militias, against an array of mostly Sunni rebel groups, including some supported by Turkey, the United States and Gulf monarchies.

Clashes, shelling and air raids in western Syria on Friday marred the first day of the ceasefire, which aims to end nearly six years of war and lead to peace talks.

The Syrian army said on Thursday that the ceasefire agreement did not cover the radical Islamist group Islamic State, fighters from the former Nusra Front, or any factions linked to them.

But several rebel officials said the agreement did include Jabhat Fateh al-Sham.