Female suicide bomber attacks Nigerian teaching college

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.