At least 23 people have been killed and 108 injured by a series of suspected suicide bombings in Maiduguri, marking one of the worst recent attacks on the capital of Borno state.

A post office, a popular weekly market and the University of Maiduguri Teaching Hospital were hit within minutes of each other at around 19:30 local time (18:30 GMT) on Monday, police in the north-eastern state say.

The sites, which are among the city's busiest locations, had drawn large crowds after the day's Ramadan fast was broken.

Nigeria's military has blamed the attack on militants from the notorious Boko Haram group.

Boko Haram originated in Maiduguri and the city became the epicentre of the Islamist group's insurgency, which began in 2009.

However, the state capital had been enjoying a relatively stable period after intensified military operations had pushed armed groups into remote border areas.

"Preliminary investigation reveals that the incidents were ​carried out by suspected suicide bombers," Borno police said in a statement, adding that an investigation was under way to establish the identity of the attackers.

Modu Bukar, a resident who witnessed the market blast and helped take victims to hospital, told the AFP news agency: "We were sitting when we suddenly heard a loud explosion. Everyone immediately started running in fear. 

"As we ran, people kept shouting that we should keep going."

Mala Mohammed, 31, told AFP that people "ran toward the post office area because the market entrance and the post office are not far apart. 

"Unfortunately, as they were running towards the post office, the person who had the explosive device ran into the crowd while people were still trying to escape."

Nigerian President Bola Tinubu condemned the attacks in a statement on Tuesday, calling them "profoundly upsetting" and the "desperate acts of the evil-minded terrorist groups".

He added that he has ordered security chiefs to move to Maiduguri and "take charge of the situation".

Just hours before the bombings, security forces repelled an overnight attack by suspected Islamist fighters on a military post in the Ajilari Cross area, on the outskirts of Maiduguri.

The scale and location of Monday's attacks - deep within the city - have shaken residents who had cautiously begun to believe that the worst years of Boko Haram's insurgency were over.

Violence has slowed from its peak around 2015 but fighters from Boko Haram and another jihadist group, Islamic State West Africa Province (Iswap), have recently stepped up attacks in north-eastern Nigeria.

Officials have warned that the threat of further violence remains, even as emergency and security agencies work to reinforce safety across the city.