Kano (Nigeria) (AFP) - A female suicide bomber killed six people at a college campus in Nigeria's Kano city on Wednesday, 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.
At about 2:30 pm (1330 GMT) on Wednesday, an assailant blew herself up at a noticeboard on the campus of the Kano Polytechnic College while students were crowded around it.
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.
- 10-year-old held -
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.
National police spokesman Frank Mba said established international "terrorist organisations" use female suicide bombers mainly because "women generally raise fewer suspicions."
The chilling trend of deploying young women and girls as bombers comes three-and-a-half months after Boko Haram kidnapped more than 200 schoolgirls from the remote town of Chibok in the northeast.
Boko Haram leader Abubakar Shekau boasted about the mass abductions in a video during which he threatened to sell the girls as slaves.
The Chibok abductions prompted a social media campaign that went viral and drew unprecedented global attention to Boko Haram's extremist uprising, which the group says is aimed at creating a strict Islamic state in the mainly Muslim north.
In the weeks following the kidnappings, some prominent jihadi websites had posts condemning the Nigerian group's extreme tactics.
- Government pledges -
Nigeria has repeatedly insisted that it knows where the girls are, while President Goodluck Jonathan and top military officials have suggested they will be brought home safely soon.
But little progress has been made in securing their release while the violence appears to be escalating across the north and centre of the country.
On Thursday in the capital Abuja, Jonathan is set to launch a fund in support of "all those who have been adversely affected by terrorism and insurgency in the country," a statement from his office said.
He hopes to raise $500 million (370 million euros) over a 12-month period from the private sector and international donors, the statement said.
More than 2,000 civilians have been killed this year, making the first half of 2014 one of the deadliest stretches of the insurgency.
Attacks had been concentrated in the remote northeast, Boko Haram's stronghold, but waves of strikes since April in major cities including Abuja have underscored the grave threat the Islamists pose to Nigeria, Africa's most populous country and top oil producer.