Afghan officials said Thursday a roadside bomb killed four civilians and wounded three others in southern Kandahar province.

Provincial officials said a tractor drove over the bomb in the Maruf district late Wednesday.

Elsewhere in southern Afghanistan Thursday, NATO said two of its service members were killed. No details were given.

The United Nations mission in Afghanistan said last week that May was the deadliest month for Afghan civilians since it began keeping track in 2007.

The U.N. said 368 civilians were killed last month, with the majority of casualties caused by the Taliban and other militants.

Elsewhere in southern Afghanistan Thursday, NATO says an insurgent attack killed one of its service members. No details were given.