At least 23 people were killed and 108 injured in suspected multiple suicide-bomb attacks in Maiduguri city, capital of Nigeria's insurgency-hit northeastern state of Borno, the state police command said in a statement late on Monday. The first blast went off at a post office in the city centre and was immediately followed by another at the popular Monday market nearby, two security sources and three Maiduguri residents told Reuters on Monday.

One blast hit the University of Maiduguri Teaching Hospital, and another struck the eastern neighbourhood of Kaleri, all in the early evening of Monday.

"Preliminary investigation reveals that the incidents were carried out by suspected suicide bombers," the state police said in the statement.

It said normalcy had been restored and security forces had tightened patrols across the city to prevent further attacks, adding that an investigation into the circumstances of the attack was underway.