Suspected members of a radical Islamist sect threw bombs at a drinking spot in Maiduguri on Sunday, killing around 25 people, witnesses and military sources said.
The attackers -- who the military said were suspected members of the Boko Haram sect -- threw three sets of explosives from the back of motorbikes at around 5 p.m. (1600 GMT) and appeared to be targeting police officers, witnesses said.
"Around 25 people have been killed in a multiple bomb blast in the Dala ward of Maiduguri," a military official said, asking not to be named.
The National Emergency Management Agency said it was working with other rescue teams to evacuate the injured but gave no further details.
Insecurity in parts of northern Nigeria has rapidly replaced militant attacks on oil infrastructure hundreds of kilometres away in the southern Niger Delta as the main security threat in Africa's most populous nation in recent months.
Boko Haram, which says it wants a wider application of strict sharia Islamic law in Nigeria, claimed responsibility for a bomb blast 10 days ago outside the national police headquarters in the capital Abuja.
The sect has been responsible for almost daily killings and attacks on police and government buildings in and around Maiduguri, which lies near Nigeria's remote northeastern borders with Chad, Cameroon and Niger.
Boko Haram's former leader, self-proclaimed Islamic scholar Mohammed Yusuf, was shot dead in police custody during a 2009 uprising in which hundreds were killed. His mosque was destroyed with tanks and the security forces claimed a decisive victory.
But low-level guerrilla attacks on police stations and assassinations, including of traditional leaders and moderate Islamic clerics, intensified in the second half of last year.
President Goodluck Jonathan, who was sworn in for his first full term in office a month ago, has voiced support for dialogue with Boko Haram.
But the group has an ill-defined command structure, a variety of people claiming to speak on its behalf, and an unknown number of followers. Some security analysts say its supporters number in the thousands.
West African Islam is overwhelmingly moderate and the sect's ideology is not widely supported by Nigeria's Muslim population, the largest in sub-Saharan Africa, but poverty and unemployment have helped it build a cult-like following.