A mysterious illness has killed more than 60 children in Cambodia since April.
The World Health Organisation says it is trying to determine whether the cases were all the same disease or a collection of illnesses.
The agency says there is no indication that it is spreading from person to person.
A virus known as EV71 has been found.
Cases have been reported in 14 provinces, mostly in southern Cambodia. The children were less than 10 years old.
They first fell ill with a high fever, followed by neurological symptoms and severe respiratory problems that quickly progressed.