A victim of a bomb blast ripped through the United Nations offices in the Nigerian capital of Abuja is loaded into an ambulance, August 26, 2011, after a car rammed into the building, and witnesses said they had seen a number of dead bodies being carried from the site. [Photo/Agencies]

ABUJA - A car bomb ripped through the United Nations' headquarters in the Nigerian capital of Abuja on Friday, killing at least 10 people, security sources and witnesses said.

They said the car rammed into the office building before exploding in an attack similar a June assault on the Abuja police headquarters claimed by Boko Haram, a Nigerian radical Islamist sect.

"We have had 10 dead and there could be more," said a medical official who declined to give his name.

The UN building was blackened from top to bottom and the remains of a car had fallen into the basement. Soldiers, firefighters and rescue workers swarmed over the area.

An Abuja-based security source said he suspected the attack was carried out by a Nigerian Islamist group, whose strikes have been growing in intensity and spreading further afield, or the North African arm of al Qaeda.

"This is very likely the work of Boko Haram and, or, AQIM (al Qaeda in the Islamic Maghreb) and is a serious escalation in the security situation in Nigeria," the security source said. "This is the worst thing that could have happened."

This year's presidential election in Nigeria was seen as the fairest since the end of military rule but it left Africa's most populous country starkly divided between the mostly Muslim north and the largely Christian south.  

Militant attacks in the oil-producing regions of the south have subsided but the north has been hit by a round of bombings and killings by Islamist extremists, prompting fears violence could spread.

Ocilaje Michael, a member of the UN staff working at the Abuja building, said he had seen a number of dead bodies after the explosion.

"We just saw the blast coming from the building. All the people in the basement were all killed. Their bodies are littered all over the place. I saw about five dead bodies," Michael said. A Reuters witness saw dead bodies being carried into an ambulance.

Similar attack

Boko Haram, whose name translates from the local northern Hausa language as "Western education is sinful", has been behind almost daily bombings and shootings, mostly targeting police in the northeast of Africa's most populous nation.

The group claimed responsibility for a June bomb attack on the car park of the Abuja police headquarters which bore similarities to Friday's blast at the UN building.  

In that attack, a car rammed through the gates of the police headquarters in the capital and exploded, killing the bomber and narrowly missing the chief of police.

On Thursday, Boko Haram bombed a police station and raided banks in a northeastern Nigerian town, leaving 12 people dead including policemen and a soldier.

In Geneva, UN spokeswoman Alessandra Vellucci said an official at the UN information centre in Lagos, Nigeria's biggest city, had confirmed that a bomb was to blame for Friday's explosion. She had no further information and it was not clear who was responsible for the attack.

"We have deployed our policemen and anti-bomb squad. We can't establish how many casualties (there are)," a police spokesman in Abuja said.

Al Qaeda in the Islamic Maghreb operates in neighbouring Niger and has kidnapped foreign workers there. However, it was also suspected of kidnapping a Briton and an Italian in Nigeria earlier this year.

In December 2007, a car bombing at the UN building in Algiers killed at least 41 people, among them 17 UN staff. In 2003, 15 staff and seven others were killed by a bomb attack at the UN building in Baghdad.

"It's hard to be sure who is responsible," said Tom Cargill, assistant head of Africa programme at London's Chatham House think-tank.

"You have the Islamist insurgency -- Boko Haram -- who have been increasing in activity but this would be a major escalation. You also have Al Qaeda-linked elements who have been trying to move in and who Western diplomats have been increasingly worried about."