Witness says police vans have been loaded with dead bodies in focal area of Boko Haram's insurgency
A bomb blast at the entrance of the police headquarters of north-east Nigeria's Borno state has caused fatalities, witnesses and security officials said.
A police officer at the scene, who could not be named, said five police vans had been loaded with the dead.
"Many people, mostly members of the police, which include men and women, were killed in the explosion," said a witness, Ali Alhaji, in the city of Maiduguri, the focal point of an insurgency by the Islamist sect Boko Haram.
Boko Haram, which wants to create an Islamic state within Nigeria, has been blamed for hundreds of bomb and gun attacks on security forces and civilians over the past two years.
There was no immediate claim of responsibility for the bomb.
Police stations are a favourite target for the insurgency, which flared up partly in response to police brutality against its members, including its founder Mohammed Yusuf, who was killed in police custody during a crackdown in 2009.
From being a reclusive clerical movement opposed to western education in the last decade, Boko Haram has radicalised and mushroomed to become the main security threat facing Africa's top energy producer, and has linked up with other Islamist groups in the region, including al-Qaida's north Africa wing.
It is based far from oil-producing facilities in the south, although its fighters have successfully targeted the capital, Abuja, in the middle of the country a handful of times.
Nigerian forces said they had shot dead 16 suspected militants in a gun battle with Boko Haram earlier this week.