Three children have already died from avian flu in Turkey, the first human victims reported outside East Asia since H5N1 re-emerged in 2003.
The potentially deadly virus has been found in wild birds and poultry over a third of Turkey, especially in villages reaching from Istanbul at Europe's gates to Van near the Iranian and Iraqi borders.
Turkish authorities have culled 600,000 wild birds and poultry to try to contain the crisis.
The Health Ministry said initial tests on 12-year-old Fatma Ozcan, who may have died of bird flu on Sunday, were negative but doctors suspect she did in fact contract the disease.
Her brother Muhammet was in critical condition in Van, the province worst hit by the outbreak that has swept Turkey since late December.
If Fatma is confirmed to have died from the virus, it would bring the number of human cases in Turkey to 20.
The UN's Food and Agriculture Organisation experts have said the virus risked becoming a constant problem in Turkey as it is in poultry in parts of Asia. The government has set up a committee to help the $3 billion Turkish poultry sector.
The more it becomes entrenched in poultry flocks, the greater the risk that more humans will become infected. So far, the virus is reported to have infected about 150 people, killing at least 79 of them. None of those cases have involved human-to-human transmission.
In a related development, Syria culled birds at a market near the Turkish border on Sunday to prevent the spread of bird flu across their 490km border, though the birds showed no sign of illness, a health official said.
The virus may be spread by birds
migrating south for the winter
"Any poultry on sale in an unregulated market and any pigeons or game are now culled," said George Khoury, head of the animal health department at the Agriculture Ministry.
"No country is safe from the risk of bird flu today, especially not Syria because it shares a border with Turkey."
The birds were being traded at an unregulated market where live birds are sold every Sunday in the northeastern border town of Kameshli, he said.
Health officials also shut down the town's regular bird market and inspected poultry shops, the state news agency Sana reported.
"The city is taking precautions against the spread of bird flu," Kibrael Kourou, a city official, told Sana.
More than 18,000 birds have been tested in Syria and no human cases of bird flu have been reported, Khoury said.
Scientists have said the virus could be spread by infected birds migrating south for the winter.