Thailand confirmed four cases of people killed by bird flu - including three children and a 58-year-old woman - and another 17 suspected cases, of whom 11 had died.
The country's poultry exporting industry, the largest in Asia, has been devastated, with 26.9 million chickens having either died or been culled.
The government rejected accusations of a cover-up, after denying for weeks that H5N1 had killed thousands of chickens since late December.
Desperate attempts to control
bird flu infection
A government spokesman admitted that the country "screwed up" in its handling of the outbreak.
The virus has now been reported in 36 of Thailand's 76 provinces. However, the threat level has been reduced in 22, where the outbreaks have been declared halted.
Vietnam has suffered the highest confirmed toll with at least nine people killed by the deadly H5N1 strain.
The World Health Organisation (WHO) warned that two sisters who had died might have caught it from their brother - signalling the first possible human-to-human transmission of the disease.
China, meanwhile, denied it was the source of the outbreak, after the respected British journal "New Scientist" said it believed a poultry vaccination scheme in southern China in early 2003 was the origin and accused the government of a cover-up.
Beijing has reported suspected bird flu outbreaks in two new provinces, Gansu and Shaanxi and confirmed a previously suspected outbreak in Guangdong province.
Indonesia finally admitted on Tuesday it was suffering an outbreak of the deadly H5N1 virus strain. One death, that of a three-year-old boy in Bali, has been reported so far.
South Korea, the first country in the current outbreak to report bird flu, has destroyed 1.8 million chickens and ducks since the virus was discovered on 15 December.
The EU extended a ban on imports of Thai poultry and pet birds from Asia for six months to 15 August.
"Although the risk of importing the virus in meat or meat products is probably low, the EU wants to make sure that any possible transmission is avoided," the bloc said in a statement in Brussels on Tuesday.
The ban concerns imports of poultry from Thailand and pet birds from Cambodia, China, Indonesia, Japan, Laos, Pakistan, South Korea, Thailand and Vietnam.