At an emergency meeting EU foreign ministers called for global co-operation, after the discovery of a potentially fatal strain of the disease in Turkey and Romania, and of a suspected case in Greece.
The Foreign Secretary, Jack Straw, said there was "bound to be concern" among EU citizens, adding: "Those concerns can be allayed if they are shown that every effort is being made by the European Union and by member states effectively to co-ordinate action."
The European Health Commissioner, Markos Kyprianou, conceded that most of the 25 EU governments lack sufficient stocks of anti-viral drugs that could be used to boost resistance in the event of a pandemic.
Most avian influenza viruses do not infect humans but the H5NI strain of bird flu has proved to be an exception. It can be passed directly from birds to people, although at present it has not mutated to a form that is easily transmitted from person to person.
The H5N1 virus has infected at least 120 people and killed 60 in south-east Asia. The virus has also been detected in Turkey and Romania. The fear is that if it mutates into a form that can spread between humans, it will quickly infect millions worldwide.
Mr Kyprianou said tests are still under way to identify whether a virus detected in a bird on the Aegean island of Chios is the deadly strain. Greece has already taken precautionary measures, banning exports of living poultry, meat and other poultry products from the island to EU member states and other countries.
The authorities in Macedonia quarantined a small southern village yesterday and sent a suspect chicken sample to England for tests.
Romania said it had detected cases of suspected bird flu in the Danube delta, one of them close to the border with Ukraine. Tests were being carried out to see whether it was the H5 virus. Turkish authorities are examining the remains of 500 quails found in a field in the west of the country.
However, ministers believe that the main threat is that the virus will mutate in the Far East. Mr Kyprianou said: "The fact we have avian flu in Europe does not affect the possibility of a human influenza pandemic."
In a statement, the foreign ministers said the EU could not tackle the threat alone, arguing that "avian and pandemic influenza are global threats and call for an international co-ordinated response".
In other developments, Roche Holding AG has said it would be willing to discuss giving a production licence for its Tamiflu drug to rival firms, after coming under pressure over the limited supplies of anti-virals.
William Burns, the chief executive of Roche Pharma Division, said the need to supply adequate amounts of the anti-virals in case of a pandemic remains the company's top priority.
"We have significantly expanded production capacity internally and by working in collaboration with other companies, and we will continue to do so," he said.