The World Health Organization (WHO) said on Saturday that at least one child death had been reported following an increase of "acute hepatitis of unknown origin" in children, and at least 169 cases had been reported in children in 12 countries. 

It did not however say in which country the death had occurred.

The WHO issued the figures as health authorities around the world investigate a mysterious increase in severe cases of hepatitis, inflammation of the liver, in young children.

The U.N. health agency said that as of April 21 acute cases of hepatitis of unknown origin had been reported in the UK, the U.S., Spain, Israel, Denmark, Ireland, the Netherlands, Italy, Norway, France, Romania and Belgium. As many as 114 of the 169 cases were reported in the UK alone, where the first cases were recorded.

The cases reported were in children aged from one month to 16 years, and 17 had required liver transplantation, said the WHO. 

"It is not yet clear if there has been an increase in hepatitis cases, or an increase in awareness of hepatitis cases that occur at the expected rate but go undetected," the organization said in a statement. 

The WHO said a common cold virus known as an adenovirus had been detected in at least 74 cases. COVID-19 infection was identified in 20 of those tested and 19 cases had a COVID-19 and adenovirus co-infection.

The U.N. health agency said it was closely monitoring the situation and working with British health authorities, other member states and partners.

U.S. health officials have sent out a nationwide alert warning doctors to be on the lookout for symptoms of pediatric hepatitis, possibly linked with a cold virus, as part of a wider probe into unexplained cases of severe liver inflammation in young children.

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(With input from Reuters, AP)