France has reinforced sanitary measures to curb a wave of avian influenza cases on duck farms in the southwest, where it has broken a recent lull in outbreaks, Reuters reported, citing the French agriculture ministry on Friday.

France has been among the countries worst affected by the unprecedented spread of avian influenza - commonly called bird flu - around the world in the past year.

The disease has killed hundreds of millions of birds, disrupting supply of poultry meat and eggs while prompting some countries including France to plan vaccination campaigns for farm flocks.

Since May 4, 21 outbreaks of highly pathogenic avian influenza have been detected in southwestern France, mostly among ducks, the agriculture ministry said in a statement.

Until the past week, France had recorded no outbreaks since March 14, leading the authorities to lower its nationwide alert level from high to moderate, the ministry said.

In the southwest, flocks in the immediate vicinity of affected farms will be culled to reduce propagation risks, while enlarged sanitary buffer zones of up to 20 km (12.43 miles) have also been introduced around outbreak locations, it said.

The southwest has a large duck breeding sector for producing foie gras pate. The region was badly hit by past avian influenza waves but the ministry said it was less affected this winter after steps to reduce the concentration of the duck population.

The latest cases underscored the relevance of vaccinating flocks, the ministry said. France last month launched a tender to secure 80 million doses to be ready to start a vaccination programme in the autumn.