Barrow, Alaska: Hundreds of kilometres above the Arctic Circle, biologists working in the frosty marshes of Alaska's North Slope are keeping a lookout for migratory birds that might bring a deadly avian flu strain to the United States.

Interior Secretary Dirk Kempthorne, visiting a bird nesting site outside Barrow, reported on Tuesday that 13,000 bird samples have been tested. While some less virulent forms of the flu were found, there has been no sign of the deadly H5N1 strain, linked to the death of at least 141 people, mostly in Asia.

"I think it's going very well," Kempthorne said after he helped a volunteer biologist gather a test sample from a young Dunin shorebird at a site on Beaufort Sea, near the northernmost point in the United States.

The fowl offspring's parents likely flew here from Japan or Korea, Audrey Taylor, the volunteer, told Kempthorne.

Deborah Rocque, the bird flu testing coordinator for the US Fish and Wildlife Service in Alaska, said the programme is concentrating on testing on the North Slope and the Yukon Delta. Both are areas where tens of thousands of migratory birds nest in the summer after arriving from Asia.

"Some go straight back to Asia and some go right down the Pacific Flyway," Rocque said.