By Sybille de La Hamaide

PARIS (Reuters) -France began vaccinating ducks against bird flu on Monday to try and stem the virus that killed millions of birds worldwide, a move that prompted the United States to impose trade restrictions on French poultry imports.

France has been among the countries worst affected by an unprecedented global spread of highly pathogenic avian influenza, commonly called bird flu, that has disrupted supply of poultry meat and eggs and sent prices rocketing in many parts of the globe in the past years.

The ravages caused to its flocks, and fears that the virus could mutate into one transmissible to humans, prompted the government to launch a mandatory vaccination campaign, making it the first country in the European Union to do so.

The first shots were given on Monday morning to ducks on a farm in the Landes, a region in southwestern France, in the presence of Agriculture Minister Marc Fesneau.

"It's a moment of optimism, we have the feeling of seeing the light at the end of the tunnel," Fesneau told reporters.

Vaccination will be mandatory for all ducks on farms that have more than 250 birds and whose products are meant to be sold in the form of meat or foie gras, the agriculture ministry said in a statement.

This means that a total of 64 million ducks at 2,700 farms will need to be vaccinated over a year for a total cost of nearly 100 million euros ($105 million), of which 85% will be financed by the state, it said.

Duck and foie gras makers group CIFOG welcomed the move.

"This vaccination plan...is a world first: its goal is to protect all farmed birds and should put an end to the preventive slaughter of animals, which no one wants to live with anymore," the group said in a statement.

More and more governments have been looking at vaccination as a way to contain the highly contagious bird flu. However, trade barriers that such vaccinations can prompt have made large poultry exporters reluctant to inoculate their birds.

The United States triggered restrictions on imports of French poultry beginning Oct. 1, citing a risk of introducing the virus into the country.

Vaccinated birds may not show signs of infection, meaning it is impossible to determine whether the virus is in a flock, the U.S. Department of Agriculture said on Friday.

Despite intensive talks, Japan was also still reluctant to accept French poultry after vaccination, Fesneau said.

The bird flu vaccination drive in France will initially be limited to ducks, which are the most vulnerable to the virus and accounted for only 8% of total French poultry output in 2022.

($1 = 0.9500 euros)

(Reporting by Sybille de La Hamaide; Editing by Emelia Sithole-Matarise and Deborah Kyvrikosaios)