Scientists were closing in on identifying the virus as the deadly H5N1 strain of bird flu that has already killed more than 70 people in East Asia since 2003, said a spokeswoman for the World Health Organization in Geneva.
"If it's confirmed, these would be the first human cases outside China and Southeast Asia," WHO spokeswoman Christine McNab told the AP.
A Turkish Health Ministry official, speaking on condition of anonymity because he is not authorized to speak to the media, said the WHO lab in Britain suspected it to be H5N1 but only confirmed that it was a type of bird flu.
The WHO also is investigating whether the cases resulted from transmission between people, which could signal the start of a human pandemic, while frightened Turks rushed to pharmacies in search of medicine as well as simple gloves and masks.
Prime Minister Recep Tayyip Erdogan said people urgently needed to be educated about keeping birds, and that during Friday prayers, imams would give instructions on protecting themselves.
Preliminary tests in Turkey indicated that Fatma Kocyigit, 15, and her 14-year-old brother, Mehmet Ali, died of the H5N1 strain, McNab said. Their 11-year-old sister, Hulya, died early Friday, but it has not been confirmed if she also had the strain.
Scientists examining samples at the British laboratory have already confirmed that the virus in the H5 family and appear to be close to determining if it is the deadly H5N1, McNab said.
The Turkish tests for H5N1 "turned out to be positive, and because it's so specific it's unlikely we're dealing with false positives," said Guenael Rodier, a senior official in the communicable diseases at WHO.
The condition of a fourth Kocyigit sibling was improving. The four were hospitalized in the eastern city of Van after developing high fevers, coughing and bleeding in their throats.
Hulya Kocyigit was buried beside her brother and sister, amid the wails of their mother, Marifet. An imam, wearing a surgical mask, read prayers as men, also in masks, took her white shroud-covered body out of the coffin and lowered it into the grave.
The doctor said the youngsters most likely contracted the virus while playing with the heads of dead chickens infected with the disease. The children had reportedly tossed the chicken heads like balls inside their house in Dogubayazit, near the Iranian border.
"They played with the heads for days," Huseyin Avni Sahin, the head physician of the Van hospital, said. "They were in very, very close contact with the dead chickens."
Another child who also tested positive for H5N1 is hospitalized in Van. The child was identified as Yusuf Tunc, and it was unclear whether there was any connection with the others. Doctors said Tunc was in critical condition.
Apart from Tunc, 19 other people were hospitalized in Van with flu-like symptoms. Authorities said tests were still under way to determine whether any had contracted bird flu.
Health Ministry Undersecretary Necdet Unuvar said more than 5,000 boxes of the antiviral drug Tamiflu were sent to eastern Turkey and five artificial respiration machines were sent to the Van hospital.
In Switzerland, Tamiflu maker Roche Pharmaceuticals said it had expedited the delivery of 100,000 packs of the drug.
Authorities are closely monitoring H5N1 for fear it could mutate into a form easily passed among humans and spark a pandemic.
Another 25-30 people had come to the Van hospital for blood tests, received medical care and left, a hospital official said on condition of anonymity because he was not authorized to speak to the media.
New bird flu cases in fowl were detected in five areas in eastern and southeastern Turkey, and authorities have killed 7,000 fowl in those areas, Agriculture Minister Mehdi Eker said.
The prime minister said people must be warned against concealing birds from health workers.
"We have a problem of education, which we have to overcome urgently," Erdogan said. "Chickens, turkeys, geese ... people should not hide them."
In the Kocyigits' hometown of Dogubayazit, teams went from house to house rounding up chickens, placing them in bags and taking them away to be killed. They warned children to keep away, after several of them, thinking it was a game, also tried to round up chickens.
The corridors of a Dogubayazit hospital was packed with people wanting their children checked for bird flu.
"We're full here. Everyone is wondering if they've got it," Dr. Huseyin Yurtsever said, adding that he was sending suspicious cases to the hospital in Van.
Authorities in the southeastern province of Sanliurfa dispatched medical teams to the town of Hilvan, where bird flu in fowl has been detected, to deal with a similar panic in a clinic there.
A team of officials from WHO arrived Friday in Turkey to assess the situation.
Officials tried to calm the rising fears.
"We don't expect the disease to contaminate a large number of people," Health Minister Recep Akdag said. "We don't expect a pandemic or anything like that in Turkey, but there is a real risk for people who are in close contact with fowl."
Eker said the problem of containing bird flu in eastern Turkey is aggravated by the fact that almost every house has fowl, which stay inside homes at night when temperatures drop.
Most of those who have died from the disease so far were farm workers who came in close contact with fowl from Vietnam, Thailand and Indonesia.
Birds in Turkey, Romania, Russia and Croatia have recently tested positive for H5N1.
Authorities have said the virus was believed to have been brought by birds migrating from Caucasus regions.