Niamey - A Boko Haram attack on a village in southeastern Niger followed by clashes with the army have killed at least 21 people, mostly from the Islamists' ranks, Niger's military said Saturday.

"Seven Niger soldiers were killed and two others wounded in a Boko Haram attack on a village near Lake Chad on Friday night," a military report said. "Boko Haram lost 14 members."

The fighting took place in Karouga, near the border dividing Niger, Nigeria and Chad, a Chadian security source said.

According to the source, Boko Haram members later sought to enter Chadian territory by crossing Lake Chad, but Chadian aircraft intervened and destroyed their five boats.

Boko Haram has in recent weeks extended its violent campaign across Nigeria's northeastern border into neighbouring countries as regional forces pursue the Islamists.

The conflict centred in northeastern Nigeria has left more than 13,000 people dead.