The death toll from a mysterious bomb blast that struck a group of herders in central Nigeria on Wednesday rose to 40 from a previous 27, the local government said on Thursday.

“Now we have around 40 people who have died,” said Abdullahi Sule, governor of Nasarawa state. The blast occurred in Rukubi, on the border between Nasarawa and Benue states, in an area plagued by communal violence.

A group representing herders said on Wednesday that the explosion was the result of an attack by the Nigerian army.

“There was a rumor before that the air force carried out this bombing, but now we know that there was no air force overflight over this region,” Sule told Arise News television channel.

“It was a drone that flew over the area and dropped the bomb,” he said, without specifying who was in command.

The Nigerian Air Force spokesman did not respond to AFP’s requests on the matter.

“It was an airstrike. It killed 27 people,” Lawal Dano, a member of the Nigerian Cattle Breeders’ Association, Miyetti Allah, said on Wednesday.

“We all know that only the military has planes to carry out air strikes, and we call for a thorough investigation and necessary sanctions for those behind this,” he added.

In the past, there have been accidental military attacks on civilians in the north of the country, where the military is fighting jihadists and criminal gangs.

Disputes between cattle herders and farmers over land, grazing and water rights are common in the central and north-western regions of Nigeria.

Last week, nine people were killed by gunmen near a camp for displaced people, according to Benue state authorities.

The tensions, whose roots go back more than a century, are caused by droughts, population growth, the expansion of sedentary agriculture and poor governance.

In recent years, these conflicts have sometimes taken on an ethnic and religious dimension, with Fulani herders being Muslim and farmers mostly Christian.

Insecurity will be one of the big issues in the presidential elections scheduled for the end of February in Nigeria. As required by the Constitution, the head of state Muhammadu Buhari, a former general elected in 2015 and re-elected in 2019, is not running again.