PARIS, March 28 (Reuters) - France's agriculture ministry raised the level of risk for bird flu to moderate from low on Friday, a day after Switzerland reported its first case for two years of the deadly H5N1 strain.

With effect from Sunday, birds in France cannot be assembled in high priority zones, and birds and poultry will have to be locked up to avoid contact with wild birds, the ministry said in a statement.

It will also be prohibited to transport birds used for hunting purposes in France, it said.

Veterinary authorities in Switzerland said on Thursday a duck from Sempachersee lake had been infected with H5N1. It was Switzerland's 33rd case of bird flu.

The other 32 discovered cases of bird flu were all reported in early 2006, on Lake Geneva and Lake Constance.

France, which raised its risk alert to "high" after some wild swans infected with the highly pathogenic virus were found dead in northeast France in July 2007, regularly adjusts its alert levels.

Experts fear the H5N1 strain could mutate into a form easily transmitted from person to person, leading to a pandemic that could kill millions worldwide.

(Reporting by Tamora Vidaillet; editing by Chris Johnson)

AlertNet news is provided by