The armed forces, tipped off by intelligence officials keeping an eye on drug-trafficking movements, found a group of five men at the border with Burma in Chiang Mai's Piang Luang sub-district.

After a 30-minute gun battle, soldiers from 721st Company killed two of the group and seized 4.5 kilograms of heroin, an AK-47 rifle, a home-made pistol and two cellphones.

A Third Army Region officer said the group was under the command of the UWSA's 171 Battalion, which is run by Wei. They were supposed to hand the heroin to a Thai trader in Piang Luang, he claimed.

The UWSA is a military arm of the Wa ethnic minority, which has close relations with the Burmese military junta. The ethnic group was allowed to produce narcotics in exchange for a cease-fire agreement with the junta and providing it with assistance in fighting the other rebellious minorities along the border.

An anti-narcotics official said at least five groups were producing various kinds of drugs along the Thai-Burmese border.