Islamist extremists struck Nigeria's northern city of Maiduguri in Borno state this morning, attacking the main military barracks with gunfire and explosions.

The Ministry of Defence said that troops had repelled the insurgents and inflicted "heavy casualties."

However thousands of young men armed themselves with machetes, axes and clubs and carried out vigilante arrests of people they charged were extremists, resulting in a number of civilians being killed.

Insurgent forces fought their way into the military installation and managed to free several people detained in cells at the barracks, but most of those released were shot as they attempted to escape.

Defence Ministry spokesman Brig-Gen Christ Olukolade insisted that "some of the victims of the terrorists' fire, in their efforts to break into the detention facility, included those they came to rescue.

"The attack has been successfully repelled with heavy human casualty on the terrorists."

He said that just four soldiers had been wounded in the fighting and "hot pursuit" operations by land and air were in progress.

The military has carried out two weeks of aerial bombardments and ground assaults on forest hideouts and mountain caves along the borders with Cameroon and Chad.

Jets bombed targets in Maiduguri, destroying several homes in the Fori neighbourhood.

At least one child was killed in the bombing raids.