A Chadian military source said on Tuesday that 11 soldiers were killed in an attack on the Nigerian border by suspected Boko Haram militants.
According to Reuters, at least 17 attackers were killed in the clashes. Boko Haram frequently targets Nigeria and its neighbouring countries.
Boko Haram has been fighting a six-year insurgency, being responsible for the deaths of over 13,000 civilians and security personnel, and causing about 1.5 million people to flee their homes, in a bid to establish a state of its own in northern Nigeria.
"It was around 4 am (0300 GMT) that they attacked us by surprise," an officer who was involved in the clashes said.
More than 600 people have been killed in Nigeria alone since President Muhammadu Buhari's inauguration at the end of May.
Nigeria’s new President Muhammadu Buhari vowed to eliminate Boko Haram after he was sworn in at the end of May. He has flown to the United States to meet with President Barack Obama to ask for increased US military assistance for fighting the militant group.
Boko Haram - which has announced its allegiance to ISIS - occupied an area the size of Belgium in Nigeria last year.
Nigeria’s former President Goodluck Jonathan was accused of dithering and incompetence in containing the armed insurgency, particularly after the kidnapping of more than 200 girls from a school in the town of Chibok in April last year.
Nigeria, alongside military coalition partners of Niger, Chad and Cameroon has claimed successes in fighting Boko Haram since February, forcing the group’s fighters out of the territory it used to control.