Thailand has reported another human fatality from bird flu, bringing the total number of human deaths in the latest outbreaks of bird flu in Asia to 23.

Thailand also announced that chickens in four provinces has tested positive for bird flu, forcing the country to admit that it was not free of the virus as it announced last week. An agriculture ministry official said all poultry within a 1km-radius of each new outbreak is to be culled, reported Dow Jones News.

So far eight people have died from the disease in Thailand and 15 have died in Vietnam. More than 100 million birds have been culled across Asia in a bid to stop the spread of the disease.

The UN Food and Agriculture Organisation has warned countries not to restock poultry flocks or resume poultry trade until they are completely clear from the virus.

China has said it has had no new reports of bird flu among poultry for 29 days, but warned further outbreaks could occur once migratory birds begin their journey north, reported Reuters.

Japan meanwhile has introduced new tougher penalties for farmers who fail to report evidence of bird flu among their flocks. The decision follows accusations that a farmer in western Japan covered up the deaths of thousands of infected chickens at his farm.