Troops from Chad and Niger have retaken the northeastern Nigerian town of Damasak from Boko Haram as part of a regional offensive to combat the militants who have pledged allegiance to ISIL.

Troops from Chad and Niger have retaken the northeastern Nigerian town of Damasak from Boko Haram as part of a regional offensive to combat the militants who have pledged allegiance to ISIL.

Boko Haram had held the town near the Niger border since November, part of a swathe of territory it had seized in Nigeria's northeast, where the group's six-year insurgency has been based.

"The offensive has allowed for control to be taken of Damasak," a Chadian security source said on Monday.

According to the source, some 200 Boko Haram fighters were left dead in the offensive that began Sunday, while 10 Chadian soldiers were killed and 20 wounded.

There was however no independent verification of the casualty figures. A hospital source in Niger's Diffa, across the border from Damasak, spoke of 33 soldiers wounded, without providing their nationalities.

A Niger official in Diffa also said Damasak had been retaken after heavy fighting.

The offensive, which followed a sustained build-up of troops in southern Niger, opened up a new front in regional efforts to wipe out the terrorist group, whose six-year insurgency has spread across borders.

It also came after Boko Haram leader Abubakar Shekau pledged allegiance to ISIL in an audio message at the weekend.

More than 200 vehicles, some of them with machine guns, as well as tanks, ambulances, water tankers and transport trucks, were seen moving towards the border on Sunday, Diffa-based radio station Anfani reported.

Aircraft targeted Boko Haram positions on Saturday and early Sunday, it added, while a Diffa resident and aid worker said Sunday that troops were seen heading to the border and heavy gunfire was heard.