Chad's army said that it had killed nearly 300 Boko Haram militants and lost 27 army employees in a four-month campaign against the jihadist group that ended on Tuesday.

President Mahamat Idriss Deby Itno ordered the campaign in October after Boko Haram a attack on a base in the Lake Chad region killed 40 troops, according to an official toll released at the time.

Chad is one of four countries around Lake Chad battling Boko Haram and its allies over the past decade after the group's insurgency in Nigeria spilt over.

The conflict has left 40,000 dead across the four nations and caused two million people to flee their homes.

Military spokesman General Chanane Issakha Acheik told a press briefing that "297 terrorists" had been killed in Operation Haskanite and the army had lost 24 soldiers and three civilians. He said the operation was now over.

The 40 troops killed in the October 27 attack on the base at Ngouboua, near the Nigerian border, were not included in the latest toll.

Chad's military leader led the operation against Boko Haram for two weeks and threatened to withdraw from a joint force with Cameroon, Niger and Nigeria to battle the jihadists, arguing that it was not effective.

Idriss Deby repeated the threat after a new clash with Boko Haram fighters in November in which 15 Chad troops were killed.

Chad also ended its military cooperation accord with former colonial power France in January and all French troops have since withdrawn.

Military sources say that Turkish instructors arrived this month to train Chadian forces in the use of drones bought from Turkey.

The countless islets on Lake Chad serve as hideouts for jihadist groups, such as Boko Haram and its offshoot Islamic State in West Africa (ISWAP), who regularly attack the army and civilians. (Courtesy, excluding headline, AFP)