BANGKOK, Sept 25: The World Health Organization said on Saturday it suspected bird flu had passed from human to human in northern Thailand, marking what could be the first such transmission of the lethal virus.

"From the existing data ... we are suspecting human-to-human transmission" of bird flu, the WHO's acting Thailand representative Kumara Rai said after studying information from Kamphaeng Phet province, where a girl and boy are suspected to have died from the virus.

The 11-year-old girl's mother, who lived near Bangkok but travelled north to visit her daughter in hospital and then attend her funeral, returned to the Thai capital, where she too fell ill and died. Her death is also on the suspect list.

Laboratory tests on the three fatalities, as well as on the girl's aunt who is hospitalized with severe pneumonia, were being conducted to detect the virus that has already killed 28 people in Asia since last December.

Health Minister Sudarat Keyuraphan said Thailand has been put on full alert as a precautionary measure but quickly sought to downplay the fears, stressing preliminary test results from the aunt showed no bird flu.

"Initial test results (from the aunt) were negative, so at the moment it's a relief for the ministry concerning whether the virus has jumped from human to human or not," Sudarat said. "But we still need to double check a final test."-AFP