The Syrian government has used internationally banned cluster munitions in attacks on a besieged rebel-held suburb of Damascus, committing war crimes on "an epic scale", Amnesty International has said.

The city of Aleppo has returned to government control, a statement by the Syrian armed forces says - ending a four-year rebel hold over parts of the city.

The Syrian army says it has begun implementing a US-Russian ceasefire, but the country's most powerful insurgent groups have not yet said whether they will abide by it.