Turkish authorities sought to determine whether a 12-year-old girl who died Sunday was the country's latest victim in a bird flu outbreak among humans.

The girl had been in contact with sick birds and her 5-year-old brother, who is seriously ill, has tested positive for the deadly strain of the virus, the Health Ministry said.

Preliminary tests on the girl, Fatma Ozcan, came back negative for the deadly and virulent H5N1 strain of bird flu, the ministry said. But authorities suspected the virus caused her death and were conducting further tests.

"Fatma Ozcan was being monitored with an initial diagnoses of bird flu but despite all efforts she could not be saved," the ministry said in a statement.

Chief physician Huseyin Avni Sahin said the brother and sister, from the nearby town of Dogubayazit, were admitted to his hospital in the eastern city of Van five days ago. Both children had been in contact with fowl and apparently ate a sickened chicken, Sahin said.

"She was brought to hospital with respiration problems very late," Sahin told reporters outside the hospital. "We immediately began treatment for bird flu since she had contacted fowl. But her condition has become grave and we lost her today."

The girl's younger brother, Muhammet Ozcan, was described as in a serious condition.

Another doctor, Ahmet Faik Oner, said the boy "has a fever and the infection in his lung is light, it's not advancing."

The health ministry said the latest test results on the sick boy brought to at least 19 the number of people in Turkey known to have contracted the H5N1 strain, including three siblings who died last week in the Van hospital. Those three were from the same town as the Ozcan children.

Tests were under way in Ankara on Sunday to determine whether dozens more people hospitalized across the country with flu-like symptoms have the virus, health authorities said.

Health officials have said that all the people with confirmed H5N1 infections apparently had touched or played with birds and that there was no evidence of person-to-person infection.

The World Health Organization is examining the cases closely as it tracks how the virus may be changing. Health experts are concerned that the virus, which first appeared in Asia in 2003, could mutate into a form that is spread easily among humans.

The three fatalities in Turkey last week were the first known deaths from the virus outside Asia, where at least 77 people have died from bird flu since the outbreak began, according to WHO's tally.

Turkish authorities on Sunday continued slaughtering thousands of birds nationwide as a precaution.

The Turkish government on Saturday set up a committee to make urgent recommendations to save the country's $3 billion poultry industry, which employs about 100,000 people. At least 455,000 domestic birds have been killed, and bird flu in birds is now confirmed or suspected in 26 of Turkey's 81 provinces.