The attack was carried out in southeast Niger's Diffa region, local officials say.
"Boko Haram terrorists" raid Blabrine military base in troubled Diffa region leaving another 10 soldiers wounded, defence ministry says in statement.
An autopsy carried out on four of the dead prisoners revealed traces of a lethal substance that had caused heart attacks in some of the victims and severe asphyxiation in the others, Chad's chief prosecutor said.
"It's the first time we have lost so many men," President Idriss Deby Itno says, after visiting attack site in Lac province, which borders Niger and Nigeria.
Northern Mali's population is fast dwindling as people flee desertification, drought and armed conflict only to end up in places where they face increased competition for resources.
The Multinational Joint Task Force, comprising soldiers from several African countries, says it has "inflicted the heaviest loss in six months" on Daesh in Lake Chad area.
When the International Court of Justice handed over a contested, oil-rich peninsula to Cameroon, a decade-long nightmare began for its Nigerian residents.
In Zamfara state alone at least 3,000 lives have been lost to banditry in the last five years, a number that's double that of terror-related murders in the country.
Those killed included 63 suspected terrorists and seven soldiers in clashes following an overnight attack on a military base in Bouhama, according to a military spokesman. Boko Haram has struck inside Chad at least seven times since last year.
Two female Boko Haram suicide bombers blew themselves up and gunmen then attacked civilians in the town of N'Guigmi, said mayor.
Defence ministry says more than 200 militants were killed in air strikes and a further 87 by ground troops since a military offensive began on December 28.
Two blasts ripped through the town of Damboa in Borno state on Saturday evening targeting people returning from celebrating the Eid al Fitr holiday, in an attack bearing all the hallmarks of Boko Haram.
Subscribe to our Youtube channel for all latest in-depth, on the ground reporting from around the world.
Copyright © 2021 TRT World.