Chad said on Wednesday it was ready to actively help Cameroon fight Boko Haram militants attacking it from Nigeria, and called on other countries in the region to translate pledges of support into concrete action.

Chad's offer comes days after an appeal by Cameroon's President Paul Biya for international military help to fight the Islamist militant group that has seized swathes of northern Nigeria and is threatening neighbours who share borders with the northeastern zones occupied by Boko Haram.

Cameroon's north is now regularly attacked by the Islamists, who highlighted their regional threat this month by seizing a military base in Nigeria meant to be used by a joint force from Nigeria, Chad, Niger and Cameroon to fight them.

"Faced by this situation that seriously threatens the security and stability of Chad ... the Chadian government will not sit here and do nothing," government spokesman Hassan Sylla Bakari said in a statement on Wednesday.

"The government expresses its solidarity with Cameroon and is ready to provide active support in the courageous and determined response of its armed forces against the criminals and terrorists of Boko Haram."

The statement did not give any detail on what form the support would take but it followed a visit to Chad by Cameroon's defence minister on Wednesday. Cameroon has dispatched elite troops to its north, where militants have launched a series of raids and set up training camps. The government said it killed 143 militants in fighting on Monday.

Military sources in Niger, to the west, said gunmen suspected of being from Boko Haram killed a civilian in the village of Gaidam Tchoukou, in Diffa region.

Chad has a reputation for one of the region's best militaries and helped French forces drive al Qaeda-linked Islamists from northern Mali in 2013.

France has sought to overcome lingering distrust between the countries in the region by helping coordinate efforts against Boko Haram.

However, Boko Haram highlighted the scale of the task to pull together an effective regional response when it seized the headquarters of the regional task force whose mission is to tackle the Islamists.

"It is time for our nations to translate into clear and concrete action the goodwill we have repeatedly spoken of," the Chadian government added in its statement.