At least 65 people were killed and 10 injured after suspected Boko Haram militants opened fire at a funeral in Nigeria’s northeastern state of Borno, Al Jazeera reported on Monday, citing a local government official. The attack took place when mourners had assembled for the funeral on Saturday morning.

Muhammed Bulama, a local government chairman, suspected that the attack was in response to the killings of 11 Boko Haram fighters nearly two weeks ago by villagers in the area. “The villagers resisted the [earlier] attack, killed 11 insurgents and recovered 10 AK-47 rifles in the encounter,” Bulama was quoted as saying. “On Saturday at about 11.40 am, the insurgents came on a reprisal mission, attacking mourners at a graveyard in the area.”

Meanwhile, Bunu Bukar Mustapha, the leader of a local anti-Boko Haram militia, gave a different version of the attack, saying that 23 people had been killed while returning from the funeral and 42 died while trying to pursue the terrorists, AFP reported. President Muhammadu Buhari condemned the attack on Sunday and instructed the country’s air force and military to start air patrols and ground search operations to track down the assailants.

Boko Haram militants have frequently attacked in and around Borneo’s Nganzai district. In northeast Nigeria, the terror group’s decade-long insurgency has led to the deaths of nearly 27,000 people and the displacement of over two million.

The Boko Haram has split into two factions, one that has pledged allegiance to Abubakar Shekau and an group associated with the Islamic State outfit, according to BBC. Boko Haram, which when loosely translated means “Western education is banned” is infamous for kidnapping school children.