MILAN, April 2 (Reuters) - The deadly H5N1 strain of bird flu may spread from Indonesia, Egypt and Nigeria to other countries as it continues to circulate in Africa and Asia, the U.N."e;s Food and Agriculture Organisation (FAO) said on Monday.

"The risk of a pandemic will be with us for the foreseeable future," said the United Nations body"e;s chief veterinary officer Joseph Domenech, reiterating calls for global efforts to contain the disease.

Egypt, Indonesia and Nigeria have not been able to contain the disease, effectively making them reservoirs of the virus for possible spread to other countries, the FAO said in a statement.

Last week Indonesia announced five new deaths from bird flu, taking its reported human death toll from the H5N1 virus to 71, the highest in the world. Egypt has 32 human bird flu cases, the highest outside Asia, with 13 people dead since 2006.

Avian flu remains mainly a bird virus, but experts fear that if the H5N1 strain mutated into a form easily transmitted from person to person it could sweep the world, killing millions.

The virus has killed at least 170 people worldwide since 2003, according to the U.N."e;s World Health Organisation.

In Indonesia, only three provinces out of 33 are free from bird flu, with the disease remaining endemic in Java, Sumatra, Bali and South Sulawesi and sporadic outbreaks happening in other parts of the country, FAO said.

Indonesia"e;s large size, weak national veterinary service and lack of resources made it more difficult to control the disease.

FAO village-based disease surveillance has been operating in 130 of 444 districts, but this should be expanded to ensure full information about outbreaks nationwide, the organisation said.

It added that in Egypt the lack of compensation to farmers for culling their poultry had helped the virus keep a foothold.

In Nigeria authorities had failed to control the movement of poultry and poultry products out of infected areas, it said.

The organisation said the spread of bird flu in Bangladesh in March was not a surprise: "The virus continues circulating in the wider region and the introduction of the virus by migratory birds in the country cannot be ruled out, as it is situated on important avian flyways."

But Domenech said there had been fewer cases of bird flu so far this year than a year ago, indicating a reduction in overall viral load, and the presence of H5N1 in wild birds has been less than last year when the virus surged, particularly in Europe.