A child bomber killed six people and wounded dozens on Tuesday outside a bus station in the heartland of the Boko Haram Islamist insurgency in northeastern Nigeria.

Witnesses reported seeing a "young girl" approaching the station in the Yobe state capital Damaturu around 7:00am (0600 GMT) and refusing to be searched by security guards at the gate before blowing herself up.

Three police officers were killed in a bomb blast during a vehicle search at a checkpoint outside the northeast Nigerian city of Damaturu on Monday, police and a witness said,

Yobe state police spokesman Toyin Gbadegesin told AFP initially that two officers were among eight people who died, including two bombers.

Suspected Boko Haram Islamists attacked police in the northeast Nigerian city of Damaturu, prompting a fierce gunfight with troops, a police officer and residents said Friday.

The gunmen late Thursday stormed the city in coordinated raids, burning at least four police buildings and leaving an unspecified number of casualties, said a senior police officer, who requested anonymity.

Gunfire and explosions rocked a northeastern Nigerian city as security forces launched a pre-emptive offensive against Boko Haram Islamists, leaving three dead, police said Sunday.

The offensive on Saturday followed intelligence that the extremist group planned to attack the restive city of Damaturu again, said the deputy police spokesman of Yobe state.

An unidentified gunman has shot dead three Chadian nationals in the northeastern Nigerian city of Damaturu, hard hit by violence blamed on Islamist group Boko Haram, police said Tuesday.

The gunman armed with a rifle stole mobile phones from the Chadian masons and shot them dead on Monday in the Pompomari area of the city, a neighborhood torn in recent weeks by Islamist attacks and a military crackdown.