Lagos, Nigeria (CNN)—Nigeria on Tuesday faced international calls to bring to justice killer mobs armed with guns and knives who massacred hundreds of villagers in the country's rural heartland.

As more details of the atrocities emerged, Nigeria's acting president, Goodluck Jonathan, replaced his national security adviser, although it was not clear whether the move was related to the weekend violence.

At least 200 Christian villagers died in the attacks early Sunday, when groups of men with guns, machetes, and knives attacked people in three villages south of Jos, in the Plateau State, Human Rights Watch said.

Other agencies gave higher death tolls. Sani Shehu, president of the nongovernmental agency Civil Rights Congress, put the number of dead at about 485. And a Christian leader who participated in a mass burial of 67 bodies Monday in one of the towns said about 375 people were dead or still missing.

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