Ceasefire in Syria: will this a be better opportunity?
Anti-government forces and Russia traded accusations of ceasefire breaches in Syria during the second day of a shaky truce.
Russian planes attacked several sites in northern Syria, according to activists.
Meanwhile, the United Nations said it was planning to use the lull in fighting to deliver aid to 154,000 Syrians in besieged areas during the next five days.
They hope to help 1.7 million in hard-to-reach areas by the end of March.
Earlier, the UN's secretary general said the cessation of hostilities had held "by and large" since Saturday.
Ban Ki-moon also said a taskforce monitoring compliance, co-chaired by the US and Russia, would meet for the first time to evaluate alleged violations.