Maiduguri - At least seven people were killed on Thursday when a female suicide bomber blew herself up at a crowded market in northeast Nigeria, witnesses and a health official said.
The mid-afternoon attack in Biu, 180 kilometres (110 miles) south of the Borno state capital Maiduguri is the latest in a spate of similar attacks in the troubled region.
The Boko Haram group has been blamed for using women and young girls as human bombs as part of its deadly campaign to create a hardline Islamic state in the country's far northeast.
A senior security source in Maiduguri confirmed Thursday's deadly suicide blast but had no immediate details on casualties.
But multiple witnesses and a nurse at the Biu general hospital said that at least seven people were killed by the explosion.
"The market was filled with hundreds of buyers and traders when a van, loaded with goods and people... drove into the premises," said trader Auwal Yusuf.
Also read: BREAKING: Female suicide bomber attacks market in Biu
"Nobody suspected anything because it is normal for vehicles to get up to that level but as the driver was about to stop, the bomb exploded and at least seven people were seen dead."
Another witness, Zakka Emmanuel, said: "We strongly suspect that the person conveying the bomb was disguised as a passenger and boarded the vehicle.
"There were many people on board, including a woman. Some of them are traders but to my knowledge nobody knew the woman.
"I counted seven dead at the spot and more than 20 others are seriously bleeding. Shops were also affected by the... blast."
Biu is the biggest town in southern Borno and Boko Haram fighters have made repeated attempts to bomb the market, which is open on Mondays and Thursdays.
Boko Haram insurgents also bombed a police station in northeast Nigeria Thursday, as the Islamists pressed on with attacks despite a multinational offensive targeting their strongholds, witnesses and security sources said.
Separately, another attempted suicide attack was foiled outside a political office elsewhere in the embattled northeast, raising fears of growing unrest in the run-up to Nigeria's general election, which has been postponed by six weeks.
Last month, scores of insurgents tried to raid Biu but were pushed back by the military.
In November last year there were claims that civilian vigilantes put the heads of slain Boko Haram fighters on wooden spikes and drove them around the town.
The Boko Haram uprising has raged for six years, killing more than 13,000 people, and the sect has in recent months increasingly posed a regional threat.