Gamboru (Nigeria) (AFP) - Chad said Wednesday it inflicted heavy losses on Nigeria's Boko Haram, killing "over 200" Islamist militants in a border town that it wrested from the rebels in a ground offensive.

Nine Chadian soldiers were also killed and 21 injured Tuesday in Gamboru as regional forces took the fight against the insurgents on to Nigerian soil for the first time, the Chadian army said.

"This toll is provisional," the Chadian military said in a statement, adding that troops were still combing the town on Nigeria's border with Cameroon for lingering rebel elements.

Around 2,000 Chadian troops backed by armoured vehicles poured across the border into Gamboru on Tuesday after the African Union last week backed a regional force to take on the extremists.

The sound of automatic gunfire could heard Wednesday in the town, which has been abandoned by residents after a barrage of air strikes by Chad in the run-up to its offensive, an AFP journalist reported.

While the operation in Gamboru continued, the town of Fotokol on the other side of the border, in Cameroon, came under fresh attack from the jihadists.

"The guys (Boko Haram) entered this morning. The fighting between them and our soldiers is very intense," a Cameroonian security source in Fotokol told AFP by telephone.

The Cameroonian troops had managed to repel the attack by mid-morning, after Chadian soldiers crossed back from Nigeria to help defend the town.





- 'Hunt them everywhere' -





In Gamboru, the clashes left scenes of desolation, with bodies lying on the ground, houses destroyed, shops gutted and trucks charred.

"We have routed this band of terrorists," the commander of the Chadian contingent Ahmat Dari told AFP Tuesday, vowing to "hunt them down everywhere."

Nigeria's military has drawn fierce criticism for failing to hold back the insurgents, who have stepped up their campaign of terror in country's northeast in the run-up to presidential and parliamentary elections on February 14.

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In recent months the group has also carried out increasing cross-border raids, threatening regional security.

Chad's intervention reflects the growing nervousness among Nigeria's neighbours over the prospect of Boko Haram achieving its stated aim of carving out an Islamic caliphate on their borders.





- Nigerian sovereignty 'intact' -





Nigerian defence spokesman Chris Olukolade denied that the presence of foreign troops on Nigerian soil compromised the country's sovereignty.

"Nigeria's territorial integrity remains intact," he said, claiming national forces had "planned and are driving the present onslaught against terrorists from all fronts in Nigeria, not the Chadian forces".

Regional forces have gone into action on several fronts.

Chadian troops and vehicles have massed near Boko Haram-held towns along Nigeria's border with Niger, pointing the way to another possible cross-border operation.

"A contingent of about 400 vehicles and tanks is stationed between Mamori and Bosso," Niger's private radio Anfani reported.





- French help -





France is supporting the operations by carrying out reconnaissance flights over border areas of Chad and Cameroon, defence officials in Paris said.

At least 13,000 people have been killed and more than a million forced from their homes since Boko Haram launched an insurgency in 2009.

The group has stepped up its attacks in recent weeks, in a move believed to be aimed at disrupting the elections.

The rebels have tried, in vain, to capture the strategic northeastern town of Maiduguri twice in the past week.

On Monday, President Goodluck Jonathan -- who is running for re-election against a former military ruler who has vowed to defeat Boko Haram -- escaped a suspected suicide bomb attack after attending a campaign rally in Gombe in the northeast.

Chad's President Idriss Deby sent soldiers to Cameroon in mid-January to assist troops from Yaounde fighting increasing rebel incursions in the country’s far northeast.

N’Djamena was already part of a long-standing regional force with Niger and Nigeria in the Lake Chad area.

But that force had been assumed to be moribund after Boko Haram overran the multi-national base in Baga, northern Borno state, on January 3, in an attack that also left hundreds of civilians feared dead.