A bomb blast near a market in the Nigerian city of Yola has killed 31 people, according to civil defence officials.
Another 38 people are being treated in hospital, said Sa'ad Bello of the National Emergency Management Agency.
There was no immediate claim of responsibility but the explosion, which came as merchants were closing shops and others were hurrying to make last-minute purchases, bore the marks of the extremist Boko Haram movement.
The group has stepped up attacks in recent weeks after a months-long lull while a multinational force drove it from the towns where it had declared an Islamic caliphate.
The explosion came after a suicide bomber exploded a car at a checkpoint outside a military barracks and killed eight soldiers in the north-eastern city of Maiduguri.
More than 60 people have been killed by bombings and rocket-propelled grenades in the city since president Muhammadu Buhari announced at his inauguration on May 29 that the command centre for the war on the Islamic extremists was moving from Abuja, the capital in central Nigeria, to the group's birthplace in Maiduguri, the capital of Borno state at the heart of the war zone.
The local government in Yola blamed the attack on Boko Haram, which has been fighting for the last six years to impose Islamic law in the north east.
It is the first such attack on the city, which has seen its population double with 300,000 refugees fleeing the insurgent violence in the north east that has killed 13,000 people and forced 1.5 million from their homes.
Deputy police superintendent Othman Abubakar said two suicide bombers were among 31 corpses recovered from the scene.
Meanwhile, the United Nations human rights chief is pressing Mr Buhari to set up independent inquiries into alleged abuses by the country's armed forces in the fight against Boko Haram.
Zeid Raad al-Hussein said people who have fled towns held by the extremist group have described "absolute terror and grave human rights violations" by the insurgents, but also reported rights violations by Nigerian armed forces.
He urged Mr Buhari to ensure that counter-insurgency operations do not result in "furthering the human rights devastation" in the north east.
Mr Zeid said he is encouraged by Mr Buhari's promise to protect human rights. He urged the president to set up inquiries into abuses, particularly "deeply disturbing allegations that thousands of people have died or been killed while held in detention by state institutions".