A female suicide bomber has killed six people at a college campus in Nigeria's Kano city, the fourth time Boko Haram Islamists were suspected of using a female attacker in as many days.
The latest violence came as the government announced the arrest of a 10-year-old girl with explosives strapped to her chest in a neighbouring area.
Boko Haram is blamed for killing more than 10,000 people since 2009 and their extreme tactics have been denounced worldwide, including on some jihadi websites.
But what appears to be a new tactic of deploying young women and girls as bombers will spur further outrage, as Nigeria seems unable to contain the violence.
The assailant on the campus of the Kano Polytechnic College blew herself up at a noticeboard where students had crammed to check their assignments for a mandatory youth civil service program.
Witness Isyaku Adamu said the explosion came from within the crush of students and left blood splattered on the ground, as soldiers and police scrambled to secure the area.
Government spokesman Mike Omeri put the casualties at six dead and six wounded, and confirmed that a female, whose age was not immediately known, was responsible for the bloodshed.
It was the fourth attack by a female bomber in Nigeria's second city since the weekend.
On Sunday, a young woman injured five police officers as she blew herself up at a another campus in the city.
The next day, two young women believed to be in their late teens or early 20s separately attacked a petrol station and a shopping centre, suicide blasts that killed at least three people and injured 13 others.
Omeri said security forces on Tuesday stopped a car in Kano's neighbouring state of Katsina and arrested three suspected Boko Haram members.
The group included one male and two girls, aged 18 and 10.
The older two tried to flee, according to Omeri's statement.
The "10-year-old ... was discovered to have been strapped with an explosive belt," he said.
