A nationwide ceasefire was mostly holding across Syria at the start of its second day on Tuesday, the Syrian Observatory for Human Rights said.

Some air attacks and shelling were reported in the first hours of the truce on Monday evening, in areas including the north Hama countryside, East Ghouta and north of Aleppo, the monitoring body said.

But that appeared to die down and the Observatory said it had not recorded a single civilian death from fighting in the fifteen hours since the ceasefire came into effect at 7 p.m. (1600 GMT) on Monday.

The ceasefire, brokered by Russia and the United States, is their second attempt this year by to halt Syria's five-year-old civil war. Russia is a major backer of Syrian President Bashar al-Assad, while the United States supports some of the rebel groups fighting to topple him.

The truce does not cover the jihadist groups Islamic State or Jabhat Fateh al-Sham, a group formerly called the Nusra Front which was al Qaeda's Syria branch until it changed its name in July.

Fighting had raged on several key fronts before the ceasefire, including Aleppo and the southern province of Quneitra on Monday, the first day of the Eid al-Adha Muslim holiday.

The Observatory said at least 31 were killed by air strikes on rebel-held Idlib province and eastern Damascus, and by bombardment of villages in the northern Homs countryside and rocket attacks in the city of Aleppo on Monday, before the truce.