The Friedrich Loeffler Institute - which made the discovery - said the strain had also been found in wild birds in Germany this week, adding that it would not be changing its bird flu risk assessment.

Isolated outbreaks on farms have been occurring despite tougher hygiene rules and orders to keep poultry indoors in high-risk areas.

The contagious H5N5 strain had been found previously in wild birds in the Netherlands, Italy, Montenegro, Italy, Croatia and Israel.

"This discovery shows how dynamic the bird flu is," state Agriculture Minister Robert Habeck said. "The virus is still present and is changing."

Different bird flu strains have also spread in Asia in recent weeks leading to the slaughter of millions of birds in South Korea and Japan, and some human infections in China.

German outbreaks are at a much lower level than in neigboring France, where a mass culling of around 800,000 ducks was undertaken after bird flu hit the southwest of the country.

The World Health Organization (WHO) this week called on all countries to monitor closely outbreaks of the bird flu and to report any human cases that could signal the start of a flu pandemic.

Experts fear the virus could mutate into a form that can spread among people.

"The rapidly expanding geographical distribution of these outbreaks and the number of virus strains currently co-circulating have put WHO on high alert," WHO Director-General Margaret Chan said on Monday. "The world is better prepared for the next influenza pandemic - following the H1N1 'mild' pandemic in 2009-2010 - but not at all well enough."

jbh/msh (Reuters, dpa)