Troops from Chad and Niger have freed two towns in northern Nigeria previously held by Boko Haram, the first gains made in a joint offensive launched at the weekend, military sources said on Monday.
About 30 Nigerien and Chadian soldiers were injured in fighting over Malam Fatouri and Damasak, a day after thousands of troops crossed the border to retake areas held by the feared armed group, whose insurgency has forced Nigeria to delay an election and neighbors to mobilize their armies.
A Chadian officer, who asked not to be named, said about 10 Chadian soldiers were killed and 20 wounded in fighting for the towns. There was no official comment from Chad's army.
"We have kicked the enemy out of these areas and they are now under our control," one of the military sources said.
Damasak, the town furthest into Nigeria, is 6 miles south of the Niger border, where Niger and Chadian troops have been massing in recent weeks ahead of the offensive.
The source said that hundreds of Boko Haram fighters had been killed in combat. There was no official confirmation of the toll and it was not possible to verify the figure.
"We had permission from Nigeria for this action," the source said. There was no immediate comment from Nigeria, which has launched its own offensive against the group, whose gains forced Nigeria to delay elections that were due in February.
Boko Haram's six-year insurgency, which aims at carving out a separate state in Nigeria's northeast, has killed thousands. The group has pledged allegiance to Islamic State of Iraq and the Levant (ISIL), which rules a self-declared caliphate in parts of Iraq and Syria, according to an audio clip posted online on Saturday.
Cameroon, Chad, Niger and Benin have this year mobilized forces to help Nigeria defeat the group after it seized swathes of territory and mounting cross-border attacks.
Nigeria and its neighbors have been working to pull together plans and rules of engagement for a regional force of 8,700 troops but cooperation between the region's armies has been strained at times.