CHATYOUT NYDANG is the leader of a Muslim militia that helps the Sudanese government wipe out Christians in southern Sudan. In July relief-and-development agency director Dennis E. Bennett spoke with an elderly southern Sudanese man in the eastern Upper Nile about life in territory that Nydang patrols.

"Routinely, anyone Chatyout's men catch walking to church is beaten and told to convert to Islam, or next time they'll be beaten harder or killed," the approximately 65-year-old Nuer tribesman, Jon Giang-giang, told Bennett.

After finding a Nuer Bible in his backpack, Nydang's men recently beat Giang-giang until he was unconscious. Bennett, executive director of Servant's Heart, says they left Giang-giang in a pit for more than two days.

Little information about abuses in the Longochok area of the eastern Upper Nile surfaced until Servant's Heart began working there five years ago. Until two years ago, before government-allied forces lost ground to southern troops, Nydang's men would ask women they encountered on isolated roads one question—are you Christian or Muslim?

"If she answered 'Muslim,' she was set free," Bennett says. "If she answered 'Christian,' she was gang-raped by 10 to 20 soldiers. Then they would cut off her breasts to leave her to bleed to death, as an example to others that this is what will happen to you unless you convert to Islam."

The government of Sudan uses such local militias in its campaign to wipe out Christians and to secure their oil-rich lands in southern Sudan. It has begun pumping oil from a well in the eastern Upper Nile.

Two decades of civil war between Sudan's Muslim north and its Christian and animist south have left 2 million people dead. Government forces regularly target civilian villages ...