GWEN IFILL: Next: bloodshed in Nigeria, as political and sectarian tensions spur a new crisis.
A warning: You may find some of the images in our story disturbing.
Victims of the massacre were buried in mass graves yesterday, one day after as many as 500 people were killed, shot and hacked to death with machetes.
This injured man said he was sleeping when the ambush came. Witnesses told of people caught in fishing nets as they ran from burning huts. Most of the victims were women and children.
DAVID KENG, eyewitness: We heard gunshots. Then, we had -- we had phone calls from the people of this area, calling -- want us to come and assist them. By the time we are nearby, we -- we heard the sound of the guns.
GWEN IFILL: The attackers struck three Christian villages near Jos, at the crossroads between Nigeria's Muslim north and its Christian south. It appeared to be retaliation for violence last January that killed more than 300 people in nearby Muslim settlements. Nigerian police said they have arrested 95 people for the Sunday attacks, and they appealed for patience.
GREGORY YENGLONG, acting police commissioner: We have no option than to ask the people to remain calm and be patient, as government steps up security.
GWEN IFILL: Thousands have died in Nigeria's religious and ethnic violence during the past decade. But the recent trouble underscores increasing instability in Africa's most populous country.
Nigeria is also a major oil exporter, sending half its output to the U.S. The vice president, Goodluck Jonathan, was named acting president last month, filling a power vacuum left when President Umaru Yar'Adua went to Saudi Arabia for medical treatment in November.
Jonathan is a Christian from the south. Yar'Adua is a Muslim from the north. Adding to the uncertainty, Yar'Adua has not been seen in public since he returned to the capital last month.
ADEMOLA ABASS, professor of international law and organizations, Brunel University: What you have now, there is no credible governance structure in the country now. And the manifestations of that dysfunctional system is what we are beginning to see in places like Jos.
GWEN IFILL: In the president's absence, Jonathan has attempted to assert control, most recently by firing his security chief. But it remains unclear that he has sufficient authority to restore calm.
The U.S., the U.N., and human rights groups called on Nigeria today to punish those behind Sunday's deadly violence.