The head of Nigeria's Christians said Saturday the killing of dozens of faithful in attacks blamed on Islamists suggested "ethnic and religious cleansing" reminiscent of the start of the 1960s civil war.

Christians will "do whatever it takes" to defend themselves, Ayo Oritsejafor, head of the Christian Association of Nigeria, said after a meeting of church leaders.

A northeastern Nigerian state where attacks on Christians left around 30 people dead was put under round-the-clock curfew Saturday amid a new wave of violence blamed on Islamists.

President Goodluck Jonathan a week ago placed parts of northeast Nigeria under emergency rule in a bid to curb escalating violence after 49 people were killed on Christmas Day, most of them at a Catholic church.

A purported spokesman for Islamist group Boko Haram on Friday claimed responsibility for separate attacks on a church and Christian mourners in Nigeria that killed around 20 people.

The spokesman who goes by the name Abul Qaqa also said the attacks were in response to an ultimatum he issued on Sunday giving Christians three days to leave the country's mainly Muslim north.

Gunmen fired on Christian mourners in northern Nigeria on Friday, killing 17 people in the latest attack to hit the region amid mounting fears of sectarian clashes, residents and a relief source said.

"There was an attack last night at Good Will Hotel in which five people were killed, all of them Igbos, and today, some friends and relatives of one of those killed in the attack gathered in his house to mourn his death," resident Zubairu Abdulaziz said of the incident in the northeastern town of Mubi, speaking of the Christian Igbo ethnic group.

Police fired tear gas and beat protesters Thursday to force them out of a square they had occupied in Nigeria's main northern city as part of demonstrations over soaring fuel prices, an organizer said.

"Around 1:15 this morning, the policemen assisted by local vigilantes fired tear gas on us, and when we refused to budge they used gun butts and cudgels to beat us while police vans ran into the crowd," Audu Bulama, one of the protest organizers, told Agence France Presse.

Gunmen have attacked a police station in northern Nigeria's Jigawa state, killing a teenage girl and wounding an officer in the first such incident since the president's state of emergency decree.

"The gunmen shot indiscriminately into the police station and engaged our men in a shootout, killing a teenage girl trying to flee and wounding a policeman," Jigawa state police commissioner Hashimu Argungu said of the attack late Tuesday.

A purported spokesman for Nigerian Islamist group Boko Haram has issued an ultimatum to Christians in the country's north and threatened to confront troops after the president declared a state of emergency in hard hit areas.

Abul Qaqa, who has spoken on behalf of the group blamed for scores of attacks in Africa's most populous nation numerous times in the past, said he was giving southerners living in the north a three-day ultimatum to leave.

At least 50 people were killed in clashes between two neighboring communities in Nigeria's southeastern Ebonyi state, a government spokesman said Sunday.

"Upwards of 50 people were killed when a group of people from Ezza community attacked residents of neighboring Ezilo community over a land dispute," the Onyekachi Eni told AFP by telephone.

Nigerian President Goodluck Jonathan on Saturday declared a state of emergency in areas hard hit by violence blamed on Islamist sect Boko Haram and ordered the closure of part of the country's borders.

He announced the measures after branding Boko Haram a "cancerous" body that was bent on destroying Africa's most populous country and vowing that the group blamed for a wave of bloody attacks would be crushed.

An explosion killed four people in the violence-torn city Nigerian city of Maiduguri as Muslim faithful left a mosque after Friday prayers, the military and residents said.

The blast comes after a series of Christmas attacks blamed on Islamist sect Boko Haram killed at least 42 people, most of them outside a Catholic church near the capital Abuja, and raised fears of reprisals from Christians.