BEIRUT, Lebanon — Half obscured by smoke and dust, a man in a video brandished a milk crate loaded with what he said were fragments of human flesh: the remains of people torn apart when a shell hit a city bus in Aleppo in northern Syria on Tuesday, the latest in a series of attacks on civilian targets by the government of President Bashar al-Assad.

“Look, look, Bashar, they are humans, they are civilians,” the man shouted as others searched for more remains among the oranges stacked in a neat pyramid on a nearby cart — a grim end to a year of civil war in which the number of Syrian refugees quintupled and the death toll doubled.

The explosion in the Tariq al-Bab area of Aleppo, which antigovernment activists said had killed at least 10 people, occurred not far from a market that was hit on Saturday. A second shell landed nearby as people tried to take the victims to hospitals, the activists said.

The international aid group Doctors Without Borders, which provides medical assistance in rebel-held northern Syria, said on Tuesday that its contacts at 10 local hospitals had counted more than 540 people killed and more than 3,000 wounded in Aleppo during two weeks of intense government bombardment that has targeted schools, residential buildings, hospitals, markets and bus stations.