ABUJA (Reuters) - Suspected members of the Islamist militant group Boko Haram killed six people in an attack on a commercial convoy being escorted by the army in Nigeria's northeastern state of Borno, the military said on Monday.

Boko Haram has killed more than 15,000 people and displaced 2.4 million across Nigeria, Cameroon, Niger and Chad during a seven-year insurgency aimed at creating a state based on a radical interpretation of Islamic law.

Nigerian army spokesman Sani Usman said suspected elements of the group who were foraging for food had ambushed troops escorting the commercial vehicles from Damboa to Maiduguri, a journey of around 50 miles (80 km).

"Unfortunately, five civilians lost their lives at the incident and another died on the way to the hospital," said Usman. "Three soldiers also sustained injuries."

Boko Haram controlled a swathe of land in northeast Nigeria around the size of Belgium at the start of last year, but has been pushed out of most of that territory by the Nigerian army, aided by troops from neighboring countries.

The militants have nevertheless continued to carry out suicide bombings in northeast Nigeria and neighboring Cameroon, Niger and Chad.

On Saturday, Niger said its soldiers and Chadian troops had killed 38 Boko Haram fighters during operations that followed attacks on two border towns in southeastern Niger.

(Reporting by Camillus Eboh; Writing by Alexis Akwagyiram; Editing by Kevin Liffey)