Caretaker Prime Minister Thak-sin Shinawatra criticised the family of the victim for concealing the deaths of their chickens from livestock authorities.

Public Health Minister Pinij Charusombat said yesterday that a laboratory test of a phlegm sample confirmed that the teenager was infected with the deadly H5N1 strain.

It was Thailand's 15th death from the virus since its outbreak in 2004. The last confirmed human case was recorded last December with the death of a five-year-old boy from Nakhon Nayok.

Pinij said the victim, who died on Monday in Phichit Provincial Hospital, was reported as using his bare hands to bury dead chickens before he became sick on July 15 with symptoms similar to those of avian flu.

Three blood tests by Phitsanulok Medical Science Centre had previously been negative for bird flu. The teenager's blood count showed he had dengue fever before yesterday's final test also confirmed H5N1.

On Tuesday, the Department of Livestock Development (DLD) said the H5N1 virus had been detected in poultry in Phichit.

All three people in the dead teenager's family have been receiving anti-viral drug Tamiflu. Pinij said that although they were in a healthy condition, public-health authorities would keep an eye on them for 14 days.

Meanwhile, Tap Klo Hospital in Phichit's Tap Klo district yesterday admitted a 9-year-old boy with symptoms similar to bird flu. Doctors are now awaiting the results of tests. The 17-year-old who died was also a resident of Thab Khlo district.

Thaksin said the latest confirmed human case represented two problems facing the country in controlling the disease - people who keep poultry in backyards not registering with livestock authorities and people failing to inform authorities about poultry deaths.

"The case in Phichit is that villagers wanted to get rid of dead chickens on their own because they were afraid the authorities would cull the rest of their birds," he said.

The victim's father, however, did not believe the disease claimed the life of his only son.

"It is a doctor who killed my son, not the bird flu. Nobody cared for him when he was there [at the hospital], but after he had died both livestock authorities and medical doctors came to see him," he said.

According to the father, after his son was diagnosed with dengue fever, he was admitted to a room containing many patients.

Meanwhile, two experts from the Department of Medical Services were assigned to Phitsanulok as a medical advisory team for doctors in four northern provinces - Phitsanulok, Phichit, Sukhothai and Kamphaeng Phet - designated by the DLD as "red zones".

DLD director-general Yukol Limlamthong defined "red zones" as areas at high risk of being infected with H5N1, not provinces confirmed as being hit by the virus.

Amid mounting reports of mysterious poultry deaths in many provinces, the DLD insisted on Tuesday that only the Bang Mun Nak district of Phichit had been hit by the H5N1 virus. The head of Phichit Provincial Livestock Office was yesterday transferred to a post in the Agriculture Ministry in Bangkok.

Dr Khamnuan Ungchusak, director of the Public Health Ministry's epidemiology office, said that, in order to ensure effectiveness in controlling an epidemic, public-health authorities would never say that the country was free from a disease.

"To keep insisting we are free from a disease would discourage people to protect themselves," he said.

Dr Paichit Warachit, director-general of the Department of Medical Science, said all 13 medical science laboratories nationwide had received blood samples of patients suspected to have caught the virus. From about 30 samples a day, almost all came out as influenza, not avian flu.

Dr Tawatch Suntracharn, director-general of the Department of Disease Control, said the ministry had stocked about one million capsules of Tamiflu. Doses had been distributed to large hospitals along with influenza test kits.