A bomb blast and gunfire shook an area around an Islamic boarding school in northern Nigeria on Sunday, leaving two of the alleged attackers dead and others wounded, emergency officials said.
It was not immediately clear who was behind the blast in the city of Zaria, but Islamist extremist group Boko Haram has been blamed for hundreds of deaths as part of its insurgency in northern and central Nigeria.
The boarding school is run by prominent Salafist cleric Awwal Adam Albani, known for outspoken criticism of Boko Haram. He was also arrested last year over a bombing and arms possession, but later released for lack of evidence.
The violence came a day ahead of commemorations marking 52 years of Nigerian independence and occurred in the hometown of Vice President Namadi Sambo, but there was no sign of a link.
Clashes began on Saturday night with an exchange of fire between gunmen and security forces in the same neighbourhood, a relief official said on condition of anonymity.
On Sunday morning, there was a report that the attackers had warned students at the boarding school to evacuate ahead of the blast, indicating the school was likely the target, said National Emergency Management Agency spokesman Yushau Shuaib.
The relief official said the blast was the result of an improvised explosive device. The complex includes the school as well as a mosque.
"Two suspects were killed," Shuaib said. "The innocent victims that were injured were taken to hospital."
Attackers and security forces exchanged gunfire after the explosion, leaving the two suspects dead, he said.
Emergency officials were not immediately able to say how many people were wounded or provide further details.
Nigeria's north has been hit by scores of bombings and shootings attributed to Boko Haram, whose insurgency is blamed for more than 1,400 deaths since 2010. A string of attacks have also hit the country's centre.
In June, two churches were attacked in Zaria and one in the city of Kaduna, both cities located in Kaduna state.
The church attacks left at least 16 people dead and sparked reprisals by Christian mobs who burned mosques and targeted Muslims, killing dozens. Boko Haram claimed responsibility for the attacks.
Muslims have often been Boko Haram's targets, though recent attacks on churches have prompted President Goodluck Jonathan to accuse the group of seeking to incite a religious crisis.
Nigeria is Africa's most populous nation and largest oil producer, roughly divided between a mainly Muslim north and predominately Christian south.
Boko Haram has claimed to be fighting for the creation of an Islamic state in Nigeria's north, though its demands have repeatedly shifted.
It is believed to have a number of factions with varying aims, in addition to imitators and criminal gangs who carry out violence under the guise of the group.
Albani and Boko Haram have been at odds in the past over a number of issues, including over the group's teachings against Western education.