GENEVA — Hundreds of people have died in fighting in eastern Ukraine since a cease-fire was agreed to by the government and armed separatists last month, the United Nations reported Wednesday, saying it had also received reports of mass graves containing hundreds of bodies.

At least 331 people were reported killed in the month after the cease-fire was announced on Sept. 5, the United Nations’ human rights office in Geneva said, adding that exchanges of artillery, tank and light arms fire had continued on an almost daily basis in some areas of the eastern regions of Donetsk and Luhansk.

The latest toll brought the number of people reported killed in the past six months to at least 3,660, including combatants and civilians, with more than 8,756 injured, Gianni Magazzeni, a senior United Nations human rights official, told reporters in Geneva. He released a 37-page report that indicated the numbers were conservative.

Most civilians deaths had been caused by indiscriminate shelling of residential areas by both pro-Russian separatists and by the Ukrainian armed forces, the report said.