GENEVA, Sept 28: The World Health Organization on Tuesday confirmed that it was examining a 'probable' first full case of human-to-human transmission of bird flu in Thailand, raising fears of a deadly global flu pandemic.

WHO officials emphasized that the outbreak among four people from a Thai village appeared to have been confined to the immediate environment of the victims, a mother and her daughter. But they could not rule out a mutation of the H5N1 bird flu virus into a more infectious form for humans until the results of tests due by the end of this week.

"There is still a possibility that the virus has mutated, but we will only know this before the end of the week when the virus has been analysed," WHO influenza and disease control expert Klaus Stohr told journalists.

Pranee Krongkaew, 26, died eight days ago and probably caught the disease while caring for her sick 11-year-old daughter, officials in Thailand said on Tuesday. The girl also died this month from suspected bird flu.

Two other people with close ties were also ill in hospital, the WHO said as health experts tried to piece together 'circumstantial evidence'. Until now, humans were thought to have caught bird flu mainly from infected poultry.

"What we're seeing in Thailand could possibly be something which is not unexpected, it could be again one of these non-sustained, inefficient, dead-end street human-to-human transmission," Mr Stohr said.

"We are concerned however, because the occurrence of such a cluster could also indicate the beginning of the more widespread, sustained, transmission of an influenza virus in humans which could lead to the global spread," he added.

Although the preliminary evidence indicated that a chain of human transmission had been broken, Mr Stohr said the fears would remain heightened until genetic tests ruled out a mutation. -AFP