A landmark truce is to take effect in Syria on Saturday, the United States and Russia announced, but the "cessation of hostilities" does not include the Islamic State and Al-Nusra Front, the main jihadist factions.

At least 25 members of Syria's al-Qaeda affiliate, al-Nusra Front, including a leader, are killed in a blast at a mosque in north-western Idlib province, activists say.

An Islamist coalition that includes Syria's al-Qaeda affiliate al-Nusra Front takes over one of the last government strongholds in western Idlib province, activists say.

Hezbollah leader Hassan Nasrallah says his Lebanese Shia group will launch an attack inside Syria on Sunni militants fighting for the al-Nusra Front.

Fresh efforts to revive peace talks on Syria is due to begin in Geneva.

The military chief of Syria's al-Nusra Front militant group is killed in an air strike, says the group