ROME (AFP) - The bird flu situation is "critical" in Indonesia, where the virus could mutate and cause a human pandemic, the UN food agency warned on Tuesday.

"The prevalence of avian influenza in Indonesia remains serious despite (national and international) containment efforts," the Rome-based Food and Agriculture Organisation said in a statement.

The FAO's chief veterinary officer, Joseph Domenech, said he was "deeply concerned that the high level of virus circulation in birds in the country could create conditions for the virus to mutate and to finally cause a human influenza pandemic."

H5N1 is endemic across nearly all of the sprawling archipelago nation, and of the total 105 human deaths reported there, 11 have occurred this year alone.

"The human mortality rate from bird flu in Indonesia is the highest in the world, and there will be more human cases if we do not focus more on containing the disease at source in animals," Domenech said.

"Indonesia is facing an uphill battle against a virus that is difficult to contain," the statement said, urging improved surveillance and control measures.

"We have also observed that new H5N1 avian influenza virus strains have recently emerged, creating the possibility that vaccines currently in use may not be fully protecting poultry against the disease," Domenech warned.