French officials have confirmed that a wild duck found dead near Lyon had the lethal H5N1 strain of bird flu - marking the first such case in France.
France has taken steps to try to stop the virus reaching its poultry
The bird's remains had been undergoing tests since it was discovered in marshland last Monday.
France - Europe's largest poultry producer - is the sixth country in the EU to suffer the deadly virus.
The H5N1 strain has killed at least 90 people around the world, mainly in South-East Asia, since 2003.
The BBC's Caroline Wyatt in Paris says France - a crossroads for migrating birds - has been on high alert over bird flu for months.
As soon as the case was suspected, the French government ordered all poultry to be either vaccinated or confined indoors to protect them from infection.
But our correspondent says French farmers already fear their livelihoods are under threat, even though no avian flu has been found in French poultry.
H5N1 bird flu can infect humans in close contact with infected birds, but there is no evidence that it can be passed from human to human.
In other developments:
- India says it has recorded its first cases of H5N1 on a farm in western Maharashtra state.
- Iran confirms its first cases of H5N1in the northern province of Gilan.
A 3-km (2-mile) safety cordon has been established around the site in Ain region where the wild duck was found, and wildlife surveillance stepped up across a 10-km area. Vets will check all birds in the zone, in accordance with EU emergency measures.
In an effort to address public concern, the French government has set up a telephone hotline and an information website as well as telling people not to handle any dead wild birds but to report them straight to the authorities.
The French case follows the confirmation of the H5N1 virus in dead swans in Austria, Germany, Slovenia, Bulgaria, Greece and Italy in the last week.
Other European countries to have confirmed outbreaks are Croatia, Romania, Ukraine and Russia.
Tests are still being carried out on two dead ducks found in the Somme region in the north of France.
Earlier this week, the EU approved a series of measures to try to halt the spread of the virus, including the automatic creation of protection and surveillance zones around outbreaks in wild birds.
If the virus transfers from wild birds to poultry, "buffer zones" that could cover an entire region could be established and the transport of poultry restricted within them.