An international human rights group has accused the Burmese army of using chemical weapons in an attack on rebel groups in the country.
The incident is alleged to have taken place near Burma's north-western border with Thailand in February.
The attack left Karenni fighters vomiting blood and unable to walk, Christian Solidarity Worldwide says.
Burma's government "completely rejected" the allegations, saying it did not have or use chemical weapons.
Christian Solidarity Worldwide says it has evidence which suggests that chemical weapons were responsible for the men's injuries.
According to accounts from Karenni fighters, who have been engaged in a long-running war with Burma's military government, the attack took place just inside the Burmese border, around 16km (10 miles) from the Thai town of Mae Hong Son.
Nyan Win said Burma had the support of all Asean nations
They claim that clouds of yellow vapour began pouring from shells fired at their positions and soon after this many of them felt sick, vomited blood and were unable to walk.
Some later suffered from blisters and acute diarrhoea.
The president of Christian Solidarity Worldwide, Australian physician Dr Martin Panter, has since flown to the area and examined five of the men.
He concluded that their symptoms were synonymous with exposure to some form of chemical attack.