At least five people have been killed in a bomb explosion in a packed mosque in Nigeria's north-eastern Borno state, a police spokesman has said. Nahum Daso told local media another 35 people were injured in the blast in the Gamboru market of Maiduguri, the state capital, during evening prayers. Unverified footage on social media appears to show the aftermath of the explosion, with people stood in a market area with dust particles in the air. No group has admitted carrying out the attack, but militants have previously targeted mosques and crowded places in the area with suicide attacks and improvised explosive devices (IED). Maiduguri has been central to an insurgency by the militant Islamist group Boko Haram and its offshoot Islamic State West Africa Province. Military operations by Boko Haram to create an Islamic caliphate in Borno state began in 2009. Security measures against the group have failed to prevent sporadic attacks against civilians in north-east Nigeria.}