A six-year-old boy has become Thailand's second victim of the bird flu outbreak, say hospital sources.
There are fears about the virus' spread
The young boy died at a hospital in central Phitsanulok province, 370 kilometres (230 miles) north of Bangkok, an official told AFP.
The first victim in Thailand to die of the virus was another six-year-old boy from the western Kanchanaburi province.
The latest death comes as neighbouring Laos confirmed tests had found the flu virus among chickens there.
"We sent samples to Hanoi for testing and we have received the result that it is H5, but we don't know the strain," an official told Reuters news agency.
China is investigating reports of a possible outbreak of the virus among its duck population.
There are fears that the bird flu virus could mutate, attaching itself to a human flu virus which could spread between people.
There are so far eight confirmed human deaths from bird flu: two in Thailand, and six in Vietnam.
Thailand is preparing to host an international conference on Wednesday to look at ways of halting the spread of the disease across Asia.
Nearly a dozen governments, including China, the European Union and the United States are due to attend, said the Thai foreign ministry.
Thailand was criticised by the EU on Monday for "non-transparency" in its dealings over the outbreak.
AVIAN FLU ALERT
First jumped "species barrier" from bird to human in 1997
In humans, symptoms include fever, sore throat, and cough
Types which threaten humans are influenza A subtypes H5N1 and H9N2
Prime Minister Thaksin Shinawatra, faced with accusations of a cover-up, has admitted his government initially kept quiet about its suspicions that avian flu had broken out, to avoid causing public panic.
Thailand has warned its death toll could be as high as six.
The second confirmed death, of another six year old boy, was made by doctors on Tuesday.
They said the child died of severe pneumonia at 1000 local time (0300 GMT).
He was admitted to hospital on 15 January following a referral from a hospital in his central province of Sukhothai, said medical officials.
They said his mother died earlier in the month, but could not confirm if she also had bird flu.
The first boy who died is believed to have picked up the virus after touching the carcasses of infected poultry in his village in western Kanchanaburi province.
His father, Chamnan Boonmanut, hit out over the government's handling of the crisis on Monday.
"The government knew, so why didn't they tell the public so that we could protect ourselves?" he said. "Nobody wants to get sick and die".
The Thai Agriculture Ministry said the virus had been detected in a further eight provinces, in addition to the first two - Sukhothai and Chachanoengsao, east of the capital Bangkok - already confirmed.
The authorities have mounted a huge operation to cull all birds in the infected areas - more than 24 million have been destroyed so far.
But as the number of such areas increases, so too are the number of angry farmers, says the BBC's Rachel Harvey in Bangkok.