“After he died his girlfriend got sick showing the same symptoms, she died also,” he added.
The Liberian government had given a death toll of nine on Friday, while the WHO had said 11.
The WHO raised the total number of confirmed total cases to 25, from 19 on Friday, and said the “majority” related to the funeral of a religious leader in Sinoe County. Cases started being registered on April 23.
The agency has confirmed that the illness is not Ebola, the haemorrhagic fever that killed thousands in a recent west African epidemic, despite some similar symptoms, nor is it Lassa fever, a virus also present in the region.
WHO spokesman Tarik Jasarevic said tests were being conducted at the US Centers for Disease Control and Prevention in Atlanta, after previous inconclusive results elsewhere.
“Field investigation teams are collecting data to establish possible association between any food and drinks served during this funeral ceremony to which all of the victims and sick people have been linked,” Jasarevic added.
The illness causes fever, vomiting, headaches and diarrhoea, but no definitive link with the deaths has yet been made.
The outbreak has stirred memories of the recent Ebola epidemic in west Africa which began in December 2013, with Liberia hit hardest: More than 29,000 are estimated to have been infected, and a third of those died.
Many Ebola survivors continue to suffer from public scorn and discrimination, exacerbated by findings that the virus can stay in some parts of the body for at least nine months after a patient has recovered.
Joanne Liu, president of medical charity Medecins Sans Frontieres (MSF), said the swift reaction to the mysterious outbreak demonstrated a positive change after the horrors of Ebola.
“People are on the starting block now when something happens, at least in terms of confirming, and I think that this sort of reactivity is the legacy of Ebola,” she told AFP.
Liu that the Liberian illness “might be food intoxication,” but that more information was needed.