Kano: A female suicide bomber injured four people at a teachers` college in northwest Nigeria on Wednesday, while the US hit back at allegations it has not done enough to tackle Boko Haram militants.
Police spokesman Ibrahim Gambari said the woman had blown herself up at the Federal College of Education in Kontagora, Niger state before reaching her target, the school library where students were revising for exams.
The blast nonetheless injured four people -- three students and a bystander.
Earlier a student at the college spoke of 10 people dead.
The attack came two days after nearly 60 people were killed in a suspected Boko Haram suicide bombing at a school in the town of Potiskum in northeast Yobe state.
The Boko Haram Islamist group is opposed to so-called "Western education" and wants to create a hardline Islamic state in northern Nigeria.
Nigerians have come to expect near daily Boko Haram attacks in the far northeast, but the latest attack will raise fresh concern if linked to the Islamist uprising.
Meanwhile the United States hit back at allegations by the Nigerian ambassador of failing to help fight the Boko Haram militants, saying there had been "a great deal" of US aid to the country.
In the past six months since the Islamic militants snatched some 200 schoolgirls in northern Nigeria, Washington has shared intelligence with the Nigerian army, begun training a new battalion and held high-level talks on the threat of Boko Haram, a US official said.
In a speech made public Tuesday, ambassador Adebowale Adefuye appeared to have taken US officials by surprise when he launched into a tirade against Washington.
But State Department spokeswoman Jen Psaki shot back that the US had "provided and approved sales of military equipment to its armed forces".
She acknowledged, however, that the US had refused to transfer some Cobra helicopters amid concerns over the Nigerian army`s ability to use them.Niger state has not been touched by the insurgency in more than two years and Kontagora is roughly 2,000 kilometres (1,200 miles) from Boko Haram`s northeastern stronghold.
At the scene of the blast, student Mary Okafor said least 10 students were killed and several others injured.
"We saw bodies on the ground between the library and the female hostel," she said.
She added that she believed there had been two bombers.
"Among the bodies were two dismembered women who we believe were the bombers," she said.
"We have all been asked to vacate the school. The authorities in the town have asked all schools to close."
On Monday`s school bombing in Yobe state, an official from the all-boys school in Potisku said the casualty toll had risen to 58 dead and 117 injured.
Police had previously put fatalities from the bombing at 47.Educational establishments in northern Nigeria have been hit several times by bombings in recent months.
On September 18, at least 13 were killed in Kano during a shootout between police and suspected suicide bombers, again at a teacher training college.
A female suicide bomber killed six people on July 30 when she detonated her explosives at a noticeboard on the campus of the Kano Polytechnic College while students were crowded around it.
That attack was the fourth by a female bomber in the city in a week and prompted the authorities to cancel public celebrations marking the end of the Muslim holy month of Ramadan.
All the bombings have been linked to Boko Haram.
The Islamist group has also bombed churches, including on Christmas Day in 2011 when 44 people were killed at the St Theresa Catholic Church in Niger`s town of Madalla.
Violence in the area has been relatively contained since, with a handful a gun attacks targeting the security forces through 2012.
Nigeria`s prolonged offensive in the northeast has become the centrepiece of its campaign against Boko Haram.
But recent violence outside the restive region, including a jailbreak in central Kogi state and Wednesday`s blast in Niger highlight the wide reach of the Islamist rebels.