Dead swans found in a Croatian nature park were infected with the lethal H5N1 bird flu strain, the agriculture ministry said Wednesday after receiving test results from a British laboratory. The laboratory in Weybridge, England, which tested samples from six swans that had already tested positive for H5 subtype of bird flu last Friday - Croatia's first bird flu case - confirmed it was the H5N1 strain, ministry spokesman Mladen Pavic said. The test results were confirmed by the European Commission in Brussels. Croatia also has stopped exporting live poultry. The six dead swans were found in the nature park of Zdenci last week and experts later found 13 more dead swans that were believed to have belonged to the same flock in a nearby fish pond. Two of those 13 also tested positive for the H5 subtype, but their samples have yet to be examined to determine whether it was the H5N1 strain. Croatia disinfected and quarantined the region around the sites and all domestic poultry there were slaughtered and incinerated. The ministry warned farmers across the country to comply with the order to keep their poultry indoors.