Germany' top state veterinary laboratory raised the risk level after more wild birds had tested positive for H5N1 in the eastern states of Saxony-Anhalt and Thuringia.

"We will raise the threat level," a spokeswoman for the Friedrich Löffler Institute told reporters.

The regional authorities in Sangerhausen in Saxony-Anhalt reported that 38 dead birds found on the shores of an artificial lake near the town of Kelbra had all tested positive. Saxony-Anhalt is the fourth of Germany's 16 states to report cases of H5N1 bird flu since late last month, when it struck down six wild birds in the southern city of Nuremberg in Bavaria.

On Tuesday, a bird found on the other side of the lake which is in Thuringia was confirmed to have had H5N1 bird flu.

Cases have also been reported near Leipzig in the neighboring eastern state of Saxony, bordering the Czech Republic which is battling a more severe outbreak of the H5N1 avian flu.

German poultry as yet unaffected

The Friedrich Löffler Institute suggested the disease could have jumped the border from the Czech side where it has infected turkey and chicken farms. So far in Germany the new outbreak has been restricted to swans, geese and other wild birds and has not affected poultry farms.

Germany battled a widespread bird flu epidemic in 2006. It broke out on the Baltic Sea island of Rügen and spread to six states, including Bavaria. The disease spread to mammals, infecting three cats and a stone marten, but did not affect humans.

In neighboring France, Europe's biggest poultry producer, authorities stepped up surveillance after tests on three dead swans confirmed an H5N1 outbreak.

Agriculture Minister Michel Barnier raised the threat level from bird flu from "moderate" to “high" following the test results on the swans that were found dead in northeast France last week.

France on high alert

It is France's second outbreak of the deadly strain of bird flu in 17 months, but Health Minister Roselyne Bachelot said there was no reason for alarm.

"France is not threatened by a bird flu pandemic as there has not been, for the moment, a human contamination from the H5N1 virus," Bachelot said.

But she added "we must be vigilant as the great flu epidemic that followed the war of 1914, the Spanish flu" came from a strain of bird flu.

Scientists believe a strain related to today's bird flu virus caused the death of tens of millions of people during the Spanish flu pandemic.

"We must do what is necessary to ensure that all of the agencies, the entire health system is ready to deal with a mutation of the virus" that could attack humans, said Bachelot on French television.

Fresh measures were ordered to ensure that chickens and other poultry did not enter into contact with wild birds and that they underwent monthly veterinary checks. Pigeon competitions have been banned and security around a one-kilometer (0.6 mile) exclusion zone established around the pond in the Moselle department where the dead swans were discovered has been beefed up.

A second 15-kilometer "observation" zone was set up around the pond at Assenoncourt but a spokesman for the local municipality said no other dead birds had been found there, which he described as a "reassuring" sign.

French poultry farms ready for lockdown

"These measures apply to all farms that must be protected from wild birds that fly overhead. These protective measures are nets and a ban on bringing birds together in public places and at markets," Barnier said.

Officials put three farms in the observation zone under quarantine, and restricted access to roads in the area.

"With these measures that we are taking, the risk of contamination will be very small," said Philippe Hestroffer, of the regional veterinary services.

A first outbreak of H5N1 in February 2006 was detected in 62 dead birds in central France and spread to a farm near the town of Versailleux where hundreds of turkeys were slaughtered. It was also the first outbreak of the virulent strain in the European Union.

France produces 900 million poultry per year including 700 million chickens, according to the Confederation of French Poultry Producers. The sector employs 80,000 people and generated four billion euros ($5.4 billion) last year.

Authorities act in the Netherlands

In the Netherlands, the authorities ordered all poultry to be kept inside. They announced the measure after what they called the discovery of a bird flu case "not far from the Netherlands."

While the bird flu virus is highly contagious among poultry and can spread to an entire flock, it remains difficult for humans to catch.

A total of 191 people worldwide have died of bird flu, according to the World Health Organization, which has reported 317 cases in its June 29 tally. Indonesia, Vietnam and Thailand top the list of most-affected countries.