Abuja 'bomber' hits Nigeria police headquarters
Two people, including a bomber, have died in an explosion at Nigeria's police headquarters in the capital, Abuja, the police say.
Police spokesman Olusola Amore said Islamist group Boko Haram was suspected of being behind the attack.
The blast in the car park of the police base destroyed many vehicles and a large plume of smoke could be seen rising from the scene.
A Red Cross spokesman told the BBC that another four bodies had been recovered.
"Six to be precise. Six bodies from the explosion," Nigerian Red Cross official Taiye Olaniyi told the BBC's Focus on Africa programme, adding that many of them had been "very badly mutilated".
Seven other people were wounded in the explosion, five of whom were being treated in hospital, the Red Cross said.
The BBC's Jonah Fisher in Lagos says that, for the Nigerian authorities, the attack is an embarrassing strike at the very heart of their security establishment.
In the last few weeks, Boko Haram, which usually operates in the north-eastern city of Maiduguri, has been stepping up its attacks on security targets.
The group said it was behind a series of bombings in the capital that took place hours after President Goodluck Jonathan's inauguration last month.
On Tuesday, Nigeria's police chief promised to decisively deal with the group by sending more troops and equipment to the north, declaring they would be finished within a few months.
"Definitely we are suspecting a group that goes by the name Boko Haram who have been issuing threats upon threats for which the police are rising up to that challenge," AFP news agency quotes Mr Amore as telling reporters after the blast.
He said the attack on the car park of the police headquarters happened at about 1000 GMT leading "to the death of the suicide bomber and a police traffic warden".
The police spokesman said a Mercedes packed with explosives had joined a police convoy that included the inspector general of police.
When the vehicles reached police headquarters the car with the bomb was diverted into an adjacent car park.
It then exploded. It is still not clear whether the driver wanted to kill himself, our reporter says.
Residents say the explosion was heard across the city.
"My windows were shaking and I heard the loud noise. I saw smoke coming up," Reuters news agency quotes one witness as telling a local television station.
A bus commuter who saw the blast told the BBC's Focus on Africa programme: "All of a sudden there was this loud explosion. Everybody was scared and people began to run around."
He said police and Red Cross officials had rushed to the scene, and had moved people away from the area.
The police said 33 cars had been damaged beyond repair and 40 more had been partially damaged by the explosion.
The BBC's Chris Ewokor at the scene said many of the cars were burnt beyond recognition.
The Boko Haram sect accuses Nigeria's government of being corrupted by Western ideas and wants to overthrow the state and impose Islamic law on the country.
It has killed dozens of people, mostly shot by gunmen riding motorbikes, in Maiduguri, the capital of Borno state.
Last year, officials blamed two explosions in Abuja during celebrations to mark the 50th anniversary of Nigeria's independence, on militants from the oil-rich Niger Delta around Port Harcourt.