By Abdoulaye Massalaki and Anne Mireille Nzouankeu
NIAMEY/YAOUNDE, Feb 9 (Reuters) - Islamist Boko Haram insurgents from Nigeria bombed a Niger border town, killing five people, and carried out attacks in neighboring Cameroon, kidnapping a bus full of passengers, military and local sources said on Monday.
The jihadist sect has killed thousands of people and kidnapped hundreds in a bid to impose its rule in northeastern Nigeria, and stepped up cross-border incursions into Cameroon.
An intensification of attacks near Lake Chad - a crossroads between Nigeria, Chad, and Niger - has sent tens of thousands of Nigerians fleeing across the borders. The escalating crisis prompted Nigeria to postpone its Feb. 14 presidential election.
With the Nigerian army struggling to contain the militants, bordering countries have launched a regional offensive against them, spurring a series of revenge attacks inside Niger and Cameroon.
Boko Haram militants stormed a prison in Diffa overnight and set off a car bomb near a customs office in the town, shortly before Niger's parliament was due to ratify participation in the regional offensive, witnesses said. Five people were killed in the bomb explosion and five others seriously injured, Niger security sources said.
Heavy gunfire carried on through the day as Niger's army repelled the assault, Boko Haram's third on Diffa in four days. A member of the national guard said about 100 suspected Boko Haram militants were in prison in Niger, but none in Diffa.
"We will defeat Boko Haram. Boko Haram has no future in this region," Nigerien President Mahamadou Issoufou told reporters on Monday in the capital Niamey. Ghana's President John Dramani Mahama said in Niamey on Monday that other African countries would offer solidarity to states affected by Boko Haram.
Authorities ordered locals to stay in their homes and mounted roadblocks around Diffa by late morning. But residents and humanitarian officials said thousands of people were fleeing from the town in cars and motorbikes.
In Cameroon, suspected Boko Haram militants attacked the northern village of Kerawa on Sunday and kidnapped at least 18 people traveling on a bus near Adanga Danga, military sources said. One said there were 30 people on board the missing bus.
Military sources in the two countries said troops had killed at least a dozen of its fighters in two days of fighting.
On Saturday, the governments of Cameroon, Chad, Niger, Nigeria and Benin agreed to establish an 8,700-strong multi-national force to take on Boko Haram.
Troops from Chad are already waging an offensive inside remote northeastern Nigerian territory and claim to have killed hundreds of Boko Haram fighters last week.
A video seen by Reuters on Monday appears to show Boko Haram leader Abubakar Shekau mocking the plans for a regional military intervention. "This message is for the people and leaders of Africa. You cannot defeat us ... Sit back and rethink. Is your constitution and democracy better than Islam?" he said. (Additional reporting by Isaac Abrak in Abuja; Writing by Joe Bavier and Emma Farge; Editing by Mark Heinrich and Dominic Evans)