Chad and Niger have launched a joint army operation against Boko Haram fighters in Nigeria, military sources say.

A source from the Niger government said the two countries had launched a "ground and air" operation against Boko Haram in northeastern Nigeria.

"We can confirm that Chadian and Nigerian forces launched an offensive this morning from Niger. The offensive is under way," Colonel Azem Bermandoa, spokesperson for Chad's army, said on Sunday.

The offensive marks Niger's first major push into Nigerian territory to combat Boko Haram. It had until now only defended itself against incursions in border areas.

Chad, backed by its air force, has already sent troops many kilometers inside northeastern Nigeria, winning back areas from the group near the Cameroon border.

So far more than 30 towns and villages have been retaken from Boko Haram since Chad and Niger joined efforts by Nigerian and Cameroonian troops to fight the group.

The fresh offensive comes after the African Union on Friday endorsed the creation of a regional force of up to 10,000 men to join the fight against the group.

PHOTO CAPTION

Nigerians walk at the Baga Solo refugee camp in Chad, Wednesday March 4, 2015

Al-Jazeera