On Tuesday, Austria and Germany became the third and fourth European Union countries to report H5N1 bird flu, just three days after the bloc's first instances were confirmed by Italy and Greece.
Germany said on Wednesday that further tests had confirmed Tuesday's preliminary findings that two dead swans found on a Baltic Sea beach were infected with the deadly strain of flu.
Reinhard Kurth, head of the Robert Koch Institute, said: "Unfortunately it has been confirmed that the swans were infected with H5N1 from Asia."
Experts had said it was only a matter of time before the H5N1 strain dangerous to humans broke out in Iran, a wintering place for wildfowl that may be carriers. Neighbouring Iraq, Azerbaijan and Turkey had already reported outbreaks.
The highly pathogenic H5N1 strain of the virus has killed at least 91 people in Asia and the Middle East, according to the World Health Organisation.
Experts fear H5N1 may mutate into a form that can spread between people and cause a pandemic that could kill millions.
New cases of H5 bird flu were found in Romania, Europe's largest wetlands and a major migratory route for wild birds.
Tests were under way in Britain to see if the new samples were H5N1, of which Romania and neighbour Bulgaria have already had cases.
Germany said it would bring forward to 17 February a ban on keeping poultry outdoors, and Italy said police had impounded more than 80,000 chickens and 7000 eggs from farms in the south that were not respecting health norms.
Across Europe and into Africa, countries have reported sharp drops in poultry sales as the number of outbreaks grows.
Hassan Mountacir, a butcher in the central market in the Moroccan capital Rabat, said: "I was buying 150 chickens every day for my stall before the flu appeared.
"Now I'm down to 10 or 20 at the most."
The bird flu virus has been
detected in wild swans
The virus could soon spread further into Europe as migrating birds return after wintering in Africa, the United Nations' Food and Agriculture Organisation (FAO) said.
Samuel Jutzi, director of the FAO's Animal Production and Health Division, told reporters in Rome: "We need to be aware that there's a real risk for Europe when the birds migrate northwards this spring."
Health experts are trying to warn people of the dangers of the virus that is contracted through direct contact with infected birds, but are struggling in countries such as Nigeria where poultry is everywhere - on the streets and on buses.
International experts are in Nigeria to advise authorities on what preventive measures they should be taking, including closing live-poultry markets and restricting poultry movements.
Fadela Chaib, a spokesperson for the World Health Organisation, said: "Above all, it is an animal disease and if one wants to avoid there being any human cases, the virus must really be stamped out in the bird population."
No human cases have been found in Nigeria, the first African country to confirm cases of H5N1, and health officials said on Tuesday that two children suspected of having the virus probably did not have it after all.
Greece also said tests on a man suspected of having bird flu had come back negative.