JAKARTA, Indonesia - The daughter of an Indonesian women who tested positive for bird flu has also contracted the virus, the World Health Organization said Wednesday, in what could be a case of human-to-human transmission.

The 14-year-old girl was in critical condition at a Jakarta hospital, WHO said on its website. The girl's 38-year-old mother has been in hospital with the bird flu virus since Jan. 26.

"She was exposed to her sick mother...and spent time in a neighbourhood where chickens and other birds were found," the WHO statement said, adding the source of infection is still under investigation.

Further tests will be needed to establish whether the daughter contracted the virus from contact with her mother or from an infected chicken or its droppings - the source of most of Indonesia's 103 fatal cases.

Cases of possible human-to-human transmission are watched closely because they increase the chance of the virus mutating into a form that is easily passed among humans, which could possibly trigger a global pandemic.

The World Health Organization said the virus passed between humans, although in a limited way, in one large cluster of cases in a single family on Indonesia's Sumatra Island in 2006.

The H5N1 strain of bird flu has killed at least 226 people worldwide since it started ravaging poultry stocks in Asia five years ago, WHO said.