(Reuters) - The US Food and Drug Administration said on Tuesday that it had found bird flu virus particles in some samples of pasteurized milk, but said that commercial milk supply remains safe.

Additional tests of milk showed that pasteurization killed the bird flu virus, federal health officials said on Friday, as Colorado became the ninth U.S. state to report an infected dairy herd.

Fragments of the bird flu virus have been found in about one fifth of commercial milk samples tested in a US nationally representative study, according to the Food and Drug Administration.