A huge explosion rocked the Niger town of Diffa on Monday, which has been previously attacked by Islamist militant group Boko Haram.

Many casualties were taken to hospital although the number of wounded in the attack is not yet known.

The bombing comes as Niger's government are due to vote on a plan to send troups to assist Nigeria against Boko Haram. Niger, Chad, Cameroon and Benin have all offered to help Nigeria create a force of up to 9,000 troops to combat the attacks by the Islamist militants who are blamed for causing 10,000 deaths in the past 12 months.

Diffa, the location of the bombing, has already been under siege in three previous attacks since Friday by Boko Haram including a fierce gunbattle that lasted until Monday morning.

Boko Haram has carried out many attacks and suicide bombings within the borders of Nigeria. But they are beginning to carry out attacks on adjacent countries, and the group have said they will attack countries joining forces with Nigeria.

On Monday, people living in northern Cameroon said three towns had been targeted by Boko Haram.

In northern Cameroon, gunmen seized a bus with 20 people on board in Koza on Sunday, driving it towards the Nigerian border 11 miles away, local resident Bouba Kaina told The Associated Press.

Boko Haram leader Abubakar Shekau sent out a fierce warning posted on a YouTube video: "You are sending 7,000 of your soldiers. Why don't you send 7 million? The 7,000 is little and we can kill them step by step ... Your soldiers are infidels and God's soldiers are victorious," he said.

Shekau also sent out a message to Idriss Deby, Chad's president, saying that he will "burn in hellfire".