BAGHDAD — Violence claimed the lives of 799 Iraqis in May, the highest monthly death toll so far this year, the United Nations said Sunday, underlining the daunting challenges the Iraqi government faces as it struggles to contain a surge in sectarian violence.

The figures issued by the United Nations mission to Iraq put last month’s civilian death toll at 603, with 196 members of security forces killed. The mission added that 1,409 Iraqis, including 1,108 civilians, were wounded. The previous month’s death toll stood at 750, making April the second deadliest month of the year.

Despite the constant militant attacks that have left a vital oil pipeline idle, Iraq’s crude oil exports increased slightly in May, the Oil Ministry said Sunday. The worst-hit city was the capital, Baghdad, with 315 people killed. The northern province of Nineveh came in second with 113, followed by nearby Salahuddin Province with 94.

The figures exclude deaths in Anbar Province, where militants have controlled parts of the provincial capital, Ramadi, and nearby Falluja since December.