Chad and Niger troops have recaptured the northeastern Nigerian town of Gachagar from Boko Haram, as part of a regional offensive to combat the Islamist insurgents, Niger's defence minister said on Thursday.

The operation in Gachagar, a town near Nigeria's border with Niger, was carried out over the past few days and involved "air and ground bombardments", Defence Minister Mahamadou Karidjo said.

He said there were "a few skirmishes" with the militants but did not give details of any casualties.

The troops will now redeploy to Malam Fatori, another border town, said Karidjo.

There has been contradictory information about the town, with Niger's army saying that Boko Haram insurgents had regrouped near Malam Fatori and the Nigerian army saying it had the situation there under control.

Regional forces have gained ground against Boko Haram in recent weeks, retaking the town of Damasak, around 30 kilometres (18 miles) from the city of Diffa in Niger.

"Targeted air strikes have been ongoing for several days against the positions of Boko Haram in Nigerian territory," an official from Diffa municipality said.

The jihadists made sweeping territorial gains in Nigeria's northeast in 2014 but appears to have been weakened by the sustained regional fight-back since February.

There are fears, however, that the group, which recently pledged allegiance to the Islamic State group, could target people during Nigeria's upcoming elections.

More than 13,000 people have been killed and some 1.5 million made homeless since Boko Haram launched its bloody insurgency in 2009.

Mounting attacks by the Nigerian militants in neighbouring countries have led the African Union to endorse the creation of an additional regional force of up to 10,000 troops to fight the group.