BANGKOK -- Seven Thai anti-drugs officials detained by an ethnic minority army allied to Myanmar's military government have been handed over to Myanmar authorities and should be home soon, officials said on Tuesday.

The military and civilian officials, missing since Sunday after crossing the border into Myanmar at the town of Tachilek, were initially detained by the United Wa State Army (UWSA), a militia blamed by Thailand for producing most of the amphetamine pills flooding the country.

"They have been released and are now staying at Tachilek under the custody of the Myanmar government, and we are contacting the Myanmar authorities to bring them back," an official at the office of Thailand's Minister for Drug Suppression told Reuters.

The seven officials from the office of the narcotics Control Board (ONCB) and the Ministry of Defence, including one female army colonel, went to Tachilek on Sunday after attending a drugs seminar in Chiang Mai, Thai officials said.

Tumnu Sirisingha, head of the ONCB's northern office, said the Thai officials got permission from Myanmar police to enter Tachilek to survey drugs problems in the town, opposite the northern Thai border town of Mae Sai.

Tumnu told reporters the group might have been captured because they were driving a suspicious looking vehicle which had heavily tinted windows and high powered radios.

"The Wa may have suspected them of spying or committing a robbery, so they captured them," he said.

The UWSA is said by thai authorities to be a major producer and supplier to Thailand of methamphetamine tablets. Officials say as many as 800 million of the Myanmar-made stimulant pills could reach Thailand this year, after 500 million last year.

Thai officials say most of the tablets are manufactured in makeshift laboratories in areas under the control of Myanmar ethnic minority groups which, like the Wa, have signed peace deals with the Yangon military government in return for relative autonomy.

The region forms part of the notorious "golden triangle" -- where the Thai, Myanmar and Laotian borders meet -- and is believed by international agencies to be one of the world's top heroin-producing regions.

Thai narcotics experts say production of methamphetamines is increasingly supplanting opium and heroin there as the main threat.