The UN's Syria envoy Staffan de Mistura says he plans to hold another round of peace talks in May. But he says the ceasefire needs to be 'revitalized' before a date can be set. De Mistura said previous talks were a success to the extent that various parties had recognised the need for a new transitional government in Syria.

But escalating violence continues to threaten the fragile truce. He called for the United States and Russia, who support different sides in the conflict, to organise a high-level Syria meeting before negotiations resume. Fighting around a hospital in Aleppo late on Wednesday is reported to have left at least 20 civilians dead.