GENEVA — Navi Pillay, the top United Nations human rights official, called Friday for “much greater urgency” in efforts to end the conflict in Syria, saying massacres carried out in recent days should spur international action.

“The increasingly brutal nature of the conflict makes international efforts to halt the bloodshed imperative,” Ms. Pillay, the high commissioner for human rights, said in a statement in Geneva. Efforts by the United States and Russia to convene an international conference on ending the two-year civil war announced this week are welcome, Ms. Pillay said, “but we need a much greater sense of urgency.”

Ms. Pillay drew attention to images of piles of bodies, including infants and small children, that purport to show the killing of dozens of civilians by pro-government militiamen in the village of Bayda and elsewhere in the Baniyas area this month. She said she believed that war crimes and crimes against humanity had been committed.

She also warned that a buildup of government forces and militia troops in the western Qusayr area near the border with Lebanon appeared to presage a government offensive and that residents were fleeing. “We’re worried, too,” said Rupert Colville, a spokesman for Ms. Pillay. “These kind of killings have not been a one-off; they’ve been repeated very savagely.”