Nine women and 52 men detained during a Myanmar army sweep in a southern border region were "safe, but to face charges", according to a report in the state mouthpiece New Light of Myanmar.
The newspaper detailed weapons seized -- including nine assault rifles, 11 "homemade" guns and a landmine -- but said no shots were fired during the raids in the country's southeastern Tanintharyi region.
"The Thai detainees have encroached upon Myanmar's territory and worked rubber farming on a commercial scale and held arms and ammunitions for their security," the English language newspaper said, adding that Thailand had been informed through "diplomatic means".
One of Thailand's deputy prime ministers, Yutthasak Sasiprapa, put the number of detained at 49 and said officials from the Thai border province of Ranong would negotiate for their release.
But he said the task would be complicated because the Myanmar army had found both illicit drugs and arms.
"They trespassed onto Myanmar soil to work and planted marijuana, while Myanmar has also seized weapons. But I am convinced they will be freed before President Thein Sein's official visit," he said, referring to the Myanmar leader's previously delayed visit to Bangkok, now set for July 22.
Many poor Myanmar nationals stream across the porous 2,400 kilometre (1,500 mile) border between the two countries in search of employment in affluent Thailand. Movement by Thais into impoverished Myanmar is rarely reported.