KANO, Nigeria — An explosion tore through a state college in the northern Nigerian city of Kano on Monday, killing at least seven people, a security source said.

The blast in the north's biggest city hit the Kano State School of Hygiene, the source said.

It was not immediately clear if Islamist militants were behind the blast. Bombings and attacks by armed insurgents now happen almost daily in Nigeria's north, where militant group Boko Haram is trying to carve out an Islamist state.

The group gained global attention in April when it abducted more than 200 girls from a rural school in northeast Nigeria, shocking people around the world for its sheer barbarity.

Kano, the north's largest city, was hit by unrest earlier this month when hundreds of youths took to the streets against a decision to appoint Nigeria's former central bank governor as the country's second-highest Islamic authority.

Amnesty International estimates that more than 1,500 people were killed in northeast Nigeria in the first three months of this year.