Pesticide poisoning was the likely cause of the mysterious deaths of at least 18 people in a southwestern Nigerian town earlier this week, the World Health Organisation said.
The "current hypothesis is cause of the event is herbicides", WHO spokesman Gregory Hartl said in a Tweet.
The victims began showing symptoms early last week in what a local government spokesman called a "mysterious disease".
This prompted fears of a new infectious disease outbreak in a region already hit by Ebola.
The victims, whose symptoms included headache, weight loss, blurred vision and loss of consciousness, died within a day of falling ill in the town of Ode-Irele, in southwestern Ondo state.
In total, 23 people had been affected.
Health officials and experts from the government and aid agencies, as well as WHO epidemiologists, had arrived in Ode-Irele to investigate the deaths.
The tests were carried out at the Lagos University Teaching Hospital, the WHO said.
