Bird flu could become endemic in Turkey and pose a serious risk to neighbouring countries, the UN Food and Agriculture Organisation has warned.
Turkey has culled more than 300,000 of its birds
Health officer Juan Lubroth said it may be spreading despite controls. More than 300,000 birds have been culled.
The UN's bird flu co-ordinator says Turkey has revealed that the best prevention is through a rapid response to outbreaks and widespread education.
Two people have died from the H5N1 strain in Turkey - 13 are in hospital.
The UN's Dr David Nabarro said $1.4bn was needed to help countries put bird flu programmes in place. He said he hoped it would be pledged at an international donors summit on bird flu to be held in Beijing on 17 and 18 January.
The FAO believes the "highly pathogenic avian influenza virus H5N1 could become endemic in Turkey".
"Far more human and animal exposure to the virus will occur if strict containment does not isolate all known and unknown locations where the virus is currently present," Mr Lubroth added.
The FAO has sent a team to Turkey to help efforts to control the virus.
It has warned neighbouring countries such as Armenia, Azerbaijan, Georgia, Iraq, Iran and Syria to be on high alert, advising them to apply surveillance and control measures and ensure the public is fully informed about the virus.
In other developments:
- The European Commission says it will extend its bird flu monitoring programme until the end of 2006. It had been due to finish at the end of January. An extra $2m has also been allocated to share the costs of laboratory tests with EU member states.
- Russia orders security measures to be stepped up at its airports and borders and its scientists warn Russians not to go to Turkey on holiday.
- Germany's Agricultural Minister Horst Seehofer says he is likely to order all birds be kept indoors.
The FAO comments came as the WHO made reassuring statements on Turkey's response to the outbreak
Dr Marc Danzon said the country's health officials had met the disease with a satisfactory response.
The WHO is trying to work out why it has spread so quickly in Turkey. The deaths were the first outside South-East Asia, where more than 70 have died since 2003.
On Tuesday, two more people were confirmed to have died of bird flu in China. They reportedly died in December - one in Guangxi province and the other in Jiangxi province.
At a news conference in Ankara, Dr Danzon said the Turkish outbreak had been taken seriously from the outset and said the WHO was working with the Turkish health ministry.
He stressed that containing the virus depended on disseminating public health information and making people abide by it.
"The people, mainly in infected areas, need to perfectly understand that the danger is contact between sick or dead poultry and a human being, mainly a child," he said.
"The worst situation is a panic situation. There is no reason to panic. With panic, there will be bad outcomes."
And he added there was "no danger" for people visiting Turkey, despite the issue of WHO travel advice.
The WHO is examining how bird flu has moved so quickly across the country since two people died in the eastern province of Van last week and why there have been so many cases.
It says there is still no evidence of human-to-human transmission of bird flu. Experts fear that development could cause a global pandemic.
Victims appeared to have contracted the virus from close contact with infected poultry. But the WHO admits it may be too soon to confirm any changes in the virus and its spread.
The WHO thinks the world is now closer to another flu pandemic than at any time since 1968, when the last of the 20th Century's three pandemics occurred.
The WHO's top official in Asia, Shigeru Omi, has stressed that East Asia remains the region at greatest risk.