Preliminary tests showed two young brothers and an adult in Ankara have a deadly strain of bird flu, the first suspected cases confirmed outside the eastern city of Van, officials said Sunday, triggering fears the virus is spreading in Turkey.

A British laboratory also confirmed the deadly strain in a 5-year-old boy, while preliminary tests in Turkey detected H5N1 in an 8-year-old girl. Both children are in intensive care in Van, about 60 miles from the Iranian border.

The cases announced Sunday raised to seven the number of cases detected since Wednesday.

A brother and sister in Van also were found to be positive for H5N1 in the preliminary tests, Health Ministry official Turan Buzgan said.

The H5N1 strain has killed at least two Turkish children in recent days — a 14-year-old boy and his 15-year-old sister — the first human fatalities from the virus outside east Asia in the current outbreak.

Tests are still being carried out to establish if a third sibling, an 11-year-old girl, also died from the virus.

If confirmed, the two children and an adult who were hospitalized in the Turkish capital, Ankara, would be the first cases of H5N1 found outside the vicinity of Van.

WHO spokeswoman Maria Cheng said from Geneva that she was aware of the report of the cases in Ankara, but that WHO had yet to be officially informed.

"We don't have any information about cases actually in the capital," Cheng told The Associated Press, adding that WHO representatives were meeting with Turkish officials and she hoped to have more information later Sunday.

Dozens of people who had recently been in close contact with fowl have been hospitalized and were being tested for bird flu across Turkey.

A delegation of WHO representatives, European health officials and Turkish Health Minister Recep Akdag traveled to Van Sunday to assess the situation.

Meanwhile, Russia's chief epidemiologist, Gennady Onishchenko, urged Russians not to travel to eastern parts of Turkey because of the bird flu outbreak, according to a statement released Sunday.

The doctor who treated the children who died said they probably contracted the illness by playing with dead chickens.

Authorities are closely watching H5N1 for fear it could mutate into a form easily passed among humans and spark a pandemic. Birds in Turkey, Romania, Russia and Croatia have recently tested positive for H5N1.

Health officials believe the best way to fight the spread of bird flu is the wholesale destruction of poultry in the affected area. But this can be difficult in places like Dogubayazit — the home town near Van of the siblings who died — where they often roam free.

"This is a disease in fowl, the people who are in contact with them are at risk," Akdag said. "This is the problem which must be addressed."

Authorities here have had difficulties explaining the danger of close contact with fowl to local residents, or the need to deliver all birds for destruction, whether or not they appear sick.

On Sunday, a group of Turkish workers in Dogubayazit had to climb over a wall when a woman refused to open the door and hand over her several chickens, insisting they were fine. The workers could not persuade her to part with the chickens and left, saying they would return with police.

It was a scene often repeated across the impoverished eastern parts of the country, where sometimes chickens are a family's most valuable possession.

But some people who realized the danger were seen inviting workers to collect their poultry in Dogubayazit Sunday. More than 30,000 fowl have been culled so far, private NTV television said Sunday.

The World Health Organization is investigating whether the disease had been transmitted from human to human, Cheng has said. But Akdag said there was no reason to suspect it had.

So far, H5N1 has been capable in rare cases of passing from poultry to humans in close contact with them, but not from human to human.

Akdag urged calm, 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.