The United Nations resumed aid convoys to besieged communities in Syria on Thursday for the first time since a deadly attack on trucks loaded with supplies on Monday.

But that accomplishment seemed fragile as talks in New York between the United States and Russia failed to produce agreement on how to restore a cease-fire in Syria, and as the Syrian military announced that it had begun a new offensive in eastern Aleppo and warned residents to stay away from rebel positions.

That announcement was made after two days of intensive bombing of eastern Aleppo by the Russian-backed Syrian forces.

A 25-truck aid convoy left Damascus on Thursday with supplies for 40,000 people in Moadamiya, a suburb of the capital, according to Jan Egeland, a United Nations special adviser for humanitarian affairs. Officials said later that the convoy had arrived in the afternoon, after delays but without incident.