Chadian armed forces have beefed up security near the border with Nigeria following a deadly attack Thursday.
A jihadist attack killed three Chadian troops and a female civilian on an island in Lake Chad early Thursday.
The attack was part of a mounting campaign by jihadists in the vast Lake Chad area, where the borders of Cameroon, Chad, Niger and Nigeria meet.
Chadian armed forces chief of staff general, Taher Erda told AFP that 21 assailants were neutralized during the attack.
On Monday, six troops were killed during an ambush on the island of Tetewa on Lake Chad. Last week, a suicide bomber killed nine civilians within the same province.