ABUJA: A bomb rocked the UN building in the Nigerian capital Abuja on Friday, killing a number of people, leaving others trapped and causing heavy damage, officials and witnesses said.

Some witnesses reported that the bomb exploded after a suspect rammed a car through the front gate. Parts of the first two floors of the building were blown out and rescue workers scrambled to rescue those left inside.

There was no immediate claim of responsibility, but an Islamist sect known as Boko Haram has been blamed for scores of bombings in recent months.

“A number of dead people and injured have been moved in ambulances to the hospital,” police spokesman Yemi Ajayi said, adding that he was unable to provide a figure for the number of casualties.

A member of the security personnel speaking on condition of anonymity spoke of “many dead.” It looks like a suicide bombing,” the source said at the scene. “A guy drove a Honda car, forced his way through the gate and rammed into the building, and then the bomb exploded.”

One UN staff member said people were still trapped in the building that sustained heavy damage.

“I don't know what is going on. Many people are still trapped upstairs and we need a crane to bring people down,” said the UN staffer who did not want to give her name.

Two cranes were later brought to the scene and rescue workers were trying to free those trapped on the upper floors.

Police said there was an explosion and UN officials said it was caused by a bomb.

“We spoke to our colleagues in Lagos, who confirmed that the explosion was caused by a bomb. But we have no further information for now,” a UN spokeswoman in Geneva told AFP.

A spokeswoman for the UN Office for the Coordination of Humanitarian Affairs meanwhile told AFP that a colleague on site had sent an SMS message to say that the explosion “appears to have come from the gate entrance to the building.”

The UN building is located in Abuja's diplomatic zone, not far from the US Embassy, and houses a number of United Nations agencies.

A bomb blast that rocked national police headquarters in Abuja in June was claimed by Boko Haram.

Most of the attacks blamed on the sect have taken place in the country's northeast, but a number have occurred elsewhere, including the previous explosion in Abuja as well as several in Suleija near the capital.

The sect launched an uprising in 2009 put down by a brutal military assault that left hundreds dead. It went dormant for about a year before reemerging in 2010 with a series of assassinations of security personnel and politicians, as well as religious and community leaders.

There have been growing concerns that the sect has formed links with extremist groups outside of Nigeria, including al Qaeda's North African branch.