STOCKHOLM, Sweden -- The European Union's infectious diseases agency on Thursday said unexplained severe cases of hepatitis in young children were "a public health event of concern".

European Centre for Disease Prevention and Control (ECDC) figures indicate that 191 hepatitis cases have been recorded worldwide since late March, most of them in Europe, with some causing liver failure and requiring transplants.

The ECDC said the disease was "quite rare" but judged the risk to children as "high" because of the potential impact. The cause is unknown.

The risk for European children cannot be accurately assessed as the evidence for transmission between humans was unclear and cases in the European Union were "sporadic with an unclear trend", it said.

But given the unknown causes of the disease and the potential severity of the illness caused, the ECDC said the outbreak "constitutes a public health event of concern".

The surge in hepatitis cases began in Scotland on March 31 and more than 100 of the 191 cases recorded so far were in Britain.

Further infections have been registered in 12 other European countries, the United States, Israel and Japan.

At least one child has died of the mysterious disease so far, according to the World Health Organization.

Most of the infected children were under 10 and many were under the age of five. None had other underlying health conditions.

The agency recommended improving surveillance and hygiene practices to stop the spread of cases.