At least 46 students have been killed by a suicide bomber at a school assembly in the north-eastern Nigerian town of Potiskum, police have said.

A suicide bomber dressed as a student is believed to have caused the blast at the boys’ school in Yobe state .

Police suggested the militant group Boko Haram carried out the attack.

Yobe state’s governor has shut all public schools around Potiskum and criticised the government for not tackling the group.

In a statement governor Ibrahim Gaidam said: “Urgent action must be taken right now to restore a fast-waning public confidence by doing whatever it takes to stop the escalating violence.”

Boko Haram has targeted schools during a deadly five-year insurgency aimed at establishing an Islamic state.

It is waging a sustained campaign to prevent children from going to school. It believes girls should not attend school and boys should only receive an Islamic education.

However thousands of people, not just schoolchildren, have been killed by the group.

On 17 October the Nigerian government claimed to have negotiated a ceasefire with Boko Haram.

But two weeks later the group’s leader, Abubakar Shekau, denied these claims and said in a video: “We have not made ceasefire with anyone. We did not negotiate with anyone. It’s a lie.”