Dr Kamnuan Uengchusak, director of the Communicable Disease Control office, said WHO have invited Thai experts to join in studying the case in which seven members of a family died of bird flu.

The latest announcement by the WHO stated that the seven fatal cases in North Sumatra, the largest cluster of infections in Indonesia, have heightened fears that the virus had passed between people.

The WHO said although humantohuman transmission could not be ruled out, the search for a possible alternative source of exposure was continuing. However, WHO said there was no evidence it had mutated into an easily transmissible form.

     The WHO's statement posted in its website said, "all confirmed cases in the cluster can be directly linked to close and prolonged exposure to a patient during a phase of severe illness."

     "To date, the investigation has found no evidence of spread within the general community and no evidence that efficient humantohuman transmission has occurred."

     The WHO said genetic sequencing revealed no evidence of significant mutations of the virus. Scientists fear a global pandemic if the virus mutates and becomes easily transmissible between humans.

    More than 120 people worldwide have died from bird flu since it reemerged as a threat in 2003 - most of them in Asia.

     Indonesia has had more bird flu deaths than any other country this year. It has the world's second highest number of fatalities since 2003, after Vietnam. Nine Indonesians who were infected have survived.

The Nation and Agence France Presse