Five new human cases of bird flu have been confirmed in several Turkish provinces, pushing the number of people infected up to 14, officials say.
Critics say the emergency bird cull has been too slow
The cases, identified as being of the deadly H5N1 strain, mean the virus is now present in the east, north and centre of the country.
At least two Turkish children have died, and correspondents say fear is spreading rapidly across the country.
Health experts say there is no sign the virus is passing from human to human.
The two siblings confirmed to have died of bird flu in the eastern town of Dogubeyazit, in the province of Van, had close contact with poultry.
Tests are still being carried out on their 11-year-old sister, who also died, to see if she was also infected with H5N1.
Their brother, the sole surviving sibling of the family, was released from hospital on Monday. Tests indicated six-year-old Ali Hasan Kocyigit did not have the virus.
The World Health Organization (WHO) has confirmed only two cases of H5N1 through its own laboratory tests in the UK, but says it considers the Turkish results reliable.
"We're certainly considering these 14 as cases and are treating them as such," the WHO's Christine McNab told the BBC News website.
She said the third death had not been added to official figures because there was still no confirmation from Turkey, but that it was being treated as a "probable additional [ie 15th] case".
International experts have gone to the region, where a mass cull of poultry is under way, to try to find out how quickly the deadly strain is spreading.
CONFIRMED TURKISH H5N1 CASES
Van - 7, including 2 deaths
Ankara - 3
Kastamonu - 2
Corum - 1
Samsun - 1
A third death is being treated as a "probable" case
But the head of the Turkey mission of the WHO, Guenael Rodier, said there was "no element in this village indicating human-to-human transmission".
The latest five cases to be reported are in the Black Sea provinces of Kastamonu, Corum and Samsun, and the eastern province of Van.
Forty-eight cases are said to be under investigation in Turkey.
The fact that the virus is now present along the Black Sea coast and central Turkey, as well as in the east, is seen as worrying.
The main concern is that the virus will mutate into a form easily transmissible between humans.
Turkish television has begun broadcasting a public health warning telling people how to protect themselves from the virus.
But Turkish Health Minister Recep Akdag - who has been visiting Van - said the problem was under control.
"There's no disease in urban areas, the only human cases are from people who've been in direct contact with poultry," he told the BBC.
The two deaths in Van last week were the first outside South East Asia, where about 70 people have been killed by the virus in the past two years.
The EU already bans imports of live birds and poultry products, including feathers, from Turkey.
On Monday, it announced a ban on feather imports from six of Turkey's neighbours: Armenia, Azerbaijan, Georgia, Iran, Iraq and Syria.
In other new cases:
- Indonesian officials confirm a 39-year-old man died of bird flu on 1 January. If confirmed by the WHO as a victim of H5N1, he would be the country's 12th fatality.
- China confirms its eight case of bird flu after a six-year-old boy in central Hunan province is treated for the H5N1 strain, Xinhua news agency says