Nigeria’s president said on Monday that at least 40 people were killed when Muslim gunmen, believed to be herders, attacked a farming community in the north-central part of the country, the latest in an increasing wave of violence in the West African country.

President Bola Tinubu also said he has ordered an investigation over the late Sunday night attack on the Zike community, extending his condolences to the victims and their families.

“I have instructed security agencies to thoroughly investigate this crisis and identify those responsible for orchestrating these violent acts,” Tinubu said in a statement late Monday.

Amnesty International said the victims, who included children and the elderly, were taken by surprise and could not flee from the gunmen.

Such attacks have become common in this part of Africa’s most populous country, where gunmen — typically herders from Fulani, a Muslim tribe — exploit security lapses to launch deadly raids on farmers in a fight over land resources.