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.
"She had similar symptoms and the clinical course of her illness was the same," Cheng said. "So it would be very probable that she died of H5N1, but right now we don't have the laboratory test to prove that."
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.
Iran restricted movement along its border to prevent the disease from spreading into the country.
The spread of the disease from East Asia, where it has killed more than 70 people, was "a concern," but the global risk assessment of a human pandemic was unchanged, she said.
"Right now these new cases in Turkey -- they don't elevate the global risk assessment, so we're still in the same pandemic alert phase that we've been in for the last couple of years," said Cheng. "But it's something that needs to be monitored very closely."
Turkish Health Minister Recep Akdag said Saturday there was no reason to suspect human-to-human transmission, and he urged calm, saying there was no risk of a pandemic.
But Dr. Gencay Gursoy, head of the Istanbul Physicians Association, said the situation was grave.
"Turkey and the world are facing the threat of a serious infection," he said.
So far, H5N1 has been capable in rare cases of transmitting from poultry to humans in close contact with them. Experts fear that if the virus should mutate to a strain that passes easily among people, it could set off a human flu pandemic.
"At the moment we don't know enough about the situation to tell whether or not the virus has changed in some way," said Cheng.
The doctor of the three siblings who died said they probably contracted the illness by playing with dead chickens.
Cheng said the area is rural, with a lot of poultry farming and that residents tend to live in close proximity to their birds. She said the cases were worrying in part because of the distance from East Asia.
"It is a jump," she said. "And if you look at how H5N1 has spread in animals, it sort of follows that pattern and implicates the role of migratory birds, because we started seeing last year H5N1 being detected in the Ural mountains, in Siberia, Mongolia, Turkey, Romania."
Authorities have culled thousands of fowl in the affected regions, but in the village of Dagdelen, on the outskirts of Dogubayazit -- the hometown of the three children who died -- villagers gathered outside an Agriculture Ministry building to complain that no one had come to cull their fowl.
In nearby Bozkurt village, local administrator Ahmet Koylu said chickens and dogs were dying but that no one had come to investigate.
On Saturday, officials reported a new bird flu case in poultry in a village near Bursa, in western Turkey, the Anatolia news agency reported.
Since January 2004, a total of 142 human cases of H5N1 infection have been reported in Vietnam, Thailand, Cambodia, Indonesia and China.
Associated Press reporters Benjamin Harvey in Dogubayazit and Selcan Hacaoglu and Suzan Fraser in Ankara contributed to this report.