The authorities were alerted on Monday about possible bird flu after the mysterious mass deaths of chickens on a farm at Sarrey, in Haute-Marne region. The farmer said his flock of 7,000 chickens appeared healthy on Saturday morning, but by evening 4,000 had died.

The cause of death is still being investigated. France is the biggest poultry producer in Western Europe. Poultry producers feared their Christmas sales could be badly affected if bird flu was confirmed.

However, the BBC's Caroline Wyatt in Paris says one theory is that the birds may have died from overheating when the ventilation for the chicken shed failed. Samples from the Sarrey farm were analysed at France's main testing laboratory in Ploufrangon.

The French authorities sealed off the farm as a precaution.

Source: BBC