GENEVA, Dec 21 (Reuters) - The World Health Organisation (WHO) suspects there has been only limited human-to-human transmission of the H5N1 virus in Pakistan, but international test results are still pending, a top official said on Friday.

David Heymann, WHO assistant director-general for health security and environment, also said that no new suspect human bird flu cases had emerged in Pakistan since Dec. 6, signalling there had been no further spread.

Global health experts fear that bird flu could mutate into a form that spreads easily from one person to another, triggering a pandemic that could kill millions of people.

Pakistan announced last week that 8 people had been infected since late October, including a veterinarian involved in culling whose two brothers died. A WHO team has investigated the outbreak, and international laboratory results on samples taken are now expected at the weekend.

"The team feels that this could be an instance of close contact human-to-human transmission in a very circumscribed area and non-sustained, just like happened in Indonesia and Thailand," Heymann told a news briefing in Geneva.

In Thailand, a mother was killed by the virus in 2004 after cradling her dying infected daughter all night. The largest known cluster of human bird flu cases worldwide occurred in May 2006 in the Karo district of Indonesia's North Sumatra province, where as many as 7 people in an extended family died.

Keiji Fukuda, coordinator of WHO's global influenza programme, told Reuters in an interview on Tuesday the cases in Pakistan are probably a combination of infections from poultry and limited person-to-person transmission due to close contact from caring for a sick loved one. (Reporting by Stephanie Nebehay; Editing by Jonathan Lynn)

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