Suspected militants killed 40 farmers in an attack on the Dumba community in Nigeria's Borno State on Sunday, a senior state official said on Monday.

Initial reports indicate the farmers strayed outside a security corridor set up by the military, venturing into an area known for insurgent activity and strewn with landmines, state commissioner of information Usman Tar said.

The militants were believed to belong to the armed group Boko Haram and its offshoot oragnisation, who have been waging a long-running insurgency in northeast Nigeria.

Security forces were looking for any farmers who had escaped the attack, Tar added.