Geneva ? Teenage siblings who died of bird flu in Turkey were the first humans outside East Asia to succumb to the deadly H5N1 strain that has apparently been spread by migratory birds, the U.N. health agency said Saturday.

A British laboratory confirmed Saturday that the 15-year-old girl and her 14-year-old brother were infected with the virus, said Maria Cheng, spokeswoman for the World Health Organization. Testing is continuing on an 11-year-old sister who died Friday.

Five WHO experts were to travel today to the city of Van, near the border with Iran, not far from the village where the three children died, to try to determine whether the disease was spread from animals or other humans.