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

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

More than 30 worshippers have been shot dead in northeast Nigeriasince Wednesday, many while praying in churches, after the expiration of an ultimatum by an Islamist sect for Christians to leave the country's mainly Muslim north.

Oritsejafor said an emergency meeting of church heads concluded "that the pattern of these killings does suggest to us a systematic ethnic and religious cleansing."

"We are reminded by the occurrences of these killings of the genesis of the civil war that took place here in Nigeria," he added, reading from a statement prepared after the meeting in the capital Abuja.

That conflict claimed more than a million lives in the late 1960s.

Nigeria's 160 million people are roughly divided between a mainly Muslim north and predominantly Christian south, but followers of both faiths have for years co-existed in the different regions.

The escalating attacks however have raised fears of reprisals.

Oritsejafor said the Christian leaders had resolved to "work out means to defend ourselves against these senseless killings.

"We have the legitimate right to defend ourselves and ... we will do whatever it takes," he added, without elaborating.

The leaders denounced the failure of state governors in the relevant areas to stop the violence.

"We hold them responsible for these heinous killings of people taking place in their states. We will not take it lightly."

Officials in Adamawa state, the scene of most of Friday's bloodshed, placed the territory under a 24-hour curfew Saturday and deployed security forces in a bid to halt the carnage.

More than 30 Christians were gunned down in three separate attacks attributed to Boko Haram in Adamawa state and neighbouring Gombe state, which were not covered by the president's state of emergency.

Eleven worshippers were killed Friday evening at a church in Adamawa's state capital Yola, and around 20 others were shot dead in Mubi town in the same state.

On Thursday evening, gunmen stormed a church in Gombe city and opened fire as worshippers prayed, killing six people including the pastor's wife.

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

But in fresh attacks over the last few days, the Islamist sect Boko Haram has targetted more Christians and a regional police headquarters.

In an address to the nation on Saturday night Jonathan said the "mindless acts of violence ... are unfortunate."

Last Sunday, a spokesman claiming to represent Boko Haram ordered Christians to leave the mainly Muslim north for the predominantly Christian south within three days.

Since then, Muslim leaders have reported that Muslims based in southern oil region of the Niger Delta have started leaving the area in apparent fear of reprisal attacks.

"Nigerian Muslims from the north have started moving out of the Niger Delta back to the north," Sheik Khalid Mohammed, head of JNI, an umbrella body for Muslims in Nigeria, told AFP.

The claims could not be independently confirmed.

In Potiskum, in Yobe state, northern Nigeria, hundreds of residents fled their homes Saturday after fierce all-night gun battles between Islamists and security forces.

Residents said a policeman and a civilian were killed when the gunmen robbed three banks. People had fled parts of Potiskum for fear of military raids in the aftermath of the attack, they added.

Boko Haram, which means "Western education is forbidden", is a shadowy group believed to have a number of factions with differing aims, including a hard-core Islamist wing.

It launched an uprising in 2009 that was put down by a brutal military operation in which some 800 people were killed.

Since the group re-emerged in 2010, it has been blamed -- and often claimed responsibility -- for a series of increasingly sophisticated and deadly attacks, including the August suicide bombing of UN headquarters in Abuja that killed 25.