At least 11 civilians were killed in Syria's second city Aleppo in one of the highest single tolls since a fragile truce came into force, a monitor says.

The first major truce in Syria's five-year civil war comes into effect, but Syrian TV says shells hit residential areas of the capital, Damascus.

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.