It is likely that a group of chickens in northern Thailand that died last week from bird flu carried the virulent H5N1 type of the virus, a Thai agricultural official said Monday.

Officials found bird flu when they conducted tests on the birds after 31 chickens died in Phichit province's Bangmunnak district, said Nirandorn Auengtrakulsuk, head of the Agriculture Ministry's Disease Control Department.

Initial findings could not determine whether it was the H5N1 type of the virus, or the more common, less deadly H5N2 type, he said.

"I personally think that it is quite certain that it is H5N1, judging from the circumstances in which the chickens died," said Nirandorn, referring to the high number of deaths.

"If it was H5N2, the number of chickens that died should not be this high," he said, adding that laboratory results confirming the type should be available within a week. Some 300 birds in the area were culled.

If confirmed, the cases would be the first found in Thai poultry in more than eight months.

Thai livestock officials said earlier this month that they were keeping a close watch for possible bird flu outbreaks in areas that have been hit by heavy rains and flooding, because the virus can live longer in wet climates.

Officials were assigned to help monitor for bird flu in seven "at risk" provinces, said Yukol Limlamthong, director of the Department of Livestock Development. They were the northern provinces of Uttaradit, Phichit, Phitsanulok and Sukhothai; and the central provinces of Suphanburi, Nakhon Pathom and Kanchanaburi.

Thai authorities culled millions of chickens and ducks when a wave of bird flu struck Asia in 2004. Thailand, one of the world's biggest chicken exporting countries, has since conducted regular surveys to check for bird flu among poultry.

The virus has been transmitted to humans who have had close contact with infected birds and carcasses, killing 14 people in Thailand, and at least 133 people in Central Asia, the Middle East, Africa and Asia, according to the World Health Organization.

For more on bird flu, visit FOXNews.com's Bird Flu Center.