Hundreds of people have been fleeing areas of north-eastern Nigeria, after a 24-hour wave of violence apparently targeting Christian communities.
At least 29 people have died in four attacks in Adamawa state, prompting the state governor to impose a curfew.
The Islamist Boko Haram group has said it carried out several attacks.
One Boko Haram faction has warned all southerners - who are mostly Christian and animist - to leave the mainly Muslim north of Nigeria.
Last week President Goodluck Jonathan declared a state of emergency in Yobe and Borno states, as well as Plateau state in central Nigeria and Niger state in the west, following a surge in ethnic and sectarian violence.
Adamawa, which borders Borno state where Boko Haram emerged, was not included.
More than 500 people have been killed by the group over the past year.
President Goodluck Jonathan, who is a Christian, said security forces would enforce the law "without fear or favour".
"I urge all Nigerians to eschew bitterness and acrimony to live together in harmony and peace," he said on Saturday in a televised address.
