Militants from the Boko Haram Islamist movement attacked Chadian troops stationed in a Nigerian border town before dawn on Wednesday before being repulsed, a Chadian military source said.

"The Boko Haram elements wanted to surprise us by attacking at about 4 am (0300 GMT). We were aware about it from the day before and were prepared," the military source told AFP.

The attack took place in Gamboru on Nigeria's border with Cameroon, where Chadian troops are deployed to help in the complex regional battle against Boko Haram have taken up positions.

"They arrived with 14 vehicles and two armored vehicles. We repulsed them and they retreated," the source said. "A helicopter was brought in to join the pursuit and destroy them."

Last week Nigeria and its neighbors — Chad, Niger, Cameroon and Benin — agreed to muster 8,700 troops, police and civilians for a wider African Union-backed force against Boko Haram.

Boko Haram launched an insurgency in Nigeria in 2009 that has now claimed the lives of more than 13,000 people.