FOTOKOL, Cameroon - Nigerian Boko Haram fighters went on the rampage in the Cameroonian border town of Fotokol Wednesday, massacring civilians and torching a mosque before being repelled by regional forces.
The onslaught came a day after Chad sent troops across the border to flush the jihadists out of the Nigerian town of Gamboru, which lies some 500 metres (yards) from Fotokol on the other side of a bridge.
Chad's army said it had killed more than 200 Boko Haram militants in the intervention - the first by regional forces against Boko Haram on its home ground.
But some of the insurgents escaped and slipped back across the border into Fotokol at dawn to make a fresh stand.
"Boko Haram inflicted so much damage here this morning. They have killed dozens of people," Umar Babakalli, a resident of Fotokol, told AFP by telephone.
Several residents said civilians' throats were slit and that the town's main mosque was torched.
"They burnt houses and killed civilians as well as soldiers," a source close to security forces said.
Another resident who had fled to another town told AFP he knew of at least 10 people who had been killed.
After several hours of clashes Cameroonian troops, backed by Chadian forces who scrambled back from Nigeria to help guard the town, managed to repel the assault.
"People are coming back little by little to assess the damage. The survivors among the attackers have left the town," a source close to the Cameroonian security services said.
No official death toll was immediately available.
On Tuesday, nine Chadian soldiers were killed and 21 were injured in Gamboru after around 2,000 troops backed by armoured vehicles poured across the border to take the fight to Boko Haram after days of clashes.
The sound of automatic gunfire could still be heard Wednesday in the town as the troops combed the town for remaining rebel elements.
The intervention came days after the African Union backed plans for a 7,500-strong five-nation regional force to take on the extremists, who control vaste swathes of northeast Nigeria.
'Hunt them everywhere'
Nigeria's military has drawn fierce criticism for failing to rein in the insurgents, who have stepped up their campaign of terror in the northeast in the run-up to presidential and parliamentary elections on February 14.
In recent months the group, which aims to establish an Islamic caliphate, has also carried out increasing cross-border raids, threatening regional security.
In Gamboru, the offensive, which was preceded by days of Chadian air strikes, had 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."
Nigerian sovereignty 'intact'
Nigeria has reacted defensively to the presence of foreign troops on its soil.
"Nigeria's territorial integrity remains intact," defence spokesman Chris Olukolade insisted, 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 on that frontier..
"A contingent of about 400 vehicles and tanks is stationed between Mamori and Bosso," Niger's private radio Anfani reported Tuesday, echoing witness accounts.
France is supporting the operations by carrying out reconnaissance flights over border areas of Chad and Cameroon to provide them with intelligence, 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.
In January the militants carried out a massacre in a town on Lake Chad that houses a regional military base.
Hundreds of civilians were reported killed in the attack, according to Amnesty International.