A suicide bomber in a car rammed into a military patrol on Sunday in the northeastern Nigerian city of Damaturu, killing himself, at least six soldiers and a civilian, the state police chief confirmed.
"He detonated the bomb he was carrying in his car, killing himself. Six soldiers were also killed, nine others were injured and are in hospital," Patrick Egbuniwe, the Yobe state police commissioner, told AFP.
"One civilian was killed and another one injured," he added.
A security source, who spoke on condition of anonymity, earlier said the attacker and five soldiers died in the explosion.
There was no immediate claim for the attack.
Egbuniwe provided a slightly different version of events, saying the suicide bomber was being chased by a military patrol vehicle and the driver detonated the bomb and blew himself up when soldiers closed in on him.
However, the security source said the bomber in a sport-utility vehicle had been parked along the roadside and rammed into the multiple vehicle military convoy when it passed, affecting two of the vehicles.
Damaturu is the capital of Yobe state, which has been hard hit by attacks blamed on radical Islamist group Boko Haram.
Sunday's attack follows a suicide bomber's attempt to assassinate Yobe state's top traditional Muslim leader, the Emir of Fika, on Friday.
The bomber sought to approach the emir after Friday prayers in the city of Potiskum but was pushed away. He blew himself up and wounded a number of others.
Authorities have been carrying out raids since the attempted attack in a bid to arrest suspected members of Boko Haram, which has claimed to be fighting for the creation of an Islamic state in Nigeria's mainly Muslim north.
The group is thought to include various factions with differing aims, however, and demands have repeatedly shifted.
In a video posted to YouTube on Saturday, the suspected leader of Boko Haram criticised US President Barack Obama over Washington's decision to label him a "global terrorist".
It was unclear when the video was made, but it marked the first time Abubakar Shekau publicly addressed the terrorist designation slapped on him by the United States in June.
In addition to Shekau, the US State Department also announced the designations for Abubakar Adam Kambar and Khalid al-Barnawi -- both who were said to be linked to Boko Haram and Al-Qaeda in the Islamic Maghreb (AQIM).
Members of Boko Haram are believed to have received training from AQIM in northern Mali, and Western countries have been watching closely for signs of further cooperation.
Some US lawmakers have been pushing Obama's administration to label Boko Haram as a whole a terrorist organisation, but American diplomats have stressed that the group remains domestically focused.
They also say deep poverty and a lack of infrastructure in Nigeria's north must be addressed as part of the solution to the violence.
Nigeria, Africa's most populous nation and largest oil producer, is roughly divided between a mainly Muslim north and predominately Christian south.