The army has been placed on high alert after major clashes between Myanmar troops and Shan rebel soldiers yesterday threatened to spill across the border.
A source at the 17th Infantry Regiment special task force in Mae Hong Son said Myanmar troops had engaged in fierce fighting with soldiers from the Shan State Army (SSA) at Doi Nak Ka, about five kilometres from the border village of Ban Rak Thai in Mae Hong Son's Muang district. The source said the army had been placed on full alert to prevent armed groups from crossing into Thailand.
The clash had erupted in the morning and was still raging yesterday evening, the source said.
The task force also sent soldiers to protect residents in border villages in case the fighting spilled over the border.
A 45-year-old villager from Ban Rak Thai said gunfire and artillery could be clearly heard coming from Myanmar, but no stray rounds had crossed the border.
Thai nationals who had gone to work on Myanmar farms were sent home.
A senior Myanmar military source said fighting broke out after the 514th Infantry Battalion learned of a large movement of SSA soldiers at Doi Nak Ka.
The Myanmar army believed the Shan soldiers were preparing to obstruct the building of a road by an army engineering unit. The road, from Tha Huayka to Ban Hua Muang, is being built in preparation for the launch of the Asean Economic Community in 2015.
The 514th Infantry Battalion sent soldiers to protect the army engineers, resulting in fierce fighting with the Shan soldiers, the source said.
In another development, businesses in Ranong want the government to rapidly resolve the problem of overlapping claims on islands in the Kraburi River between Thailand and Myanmar.
Without urgent action, the problem could escalate into a serious conflict, similar to what has happened on the Thai-Cambodia border, said Nit Aui-tengkeng, the chairman of the Federation of Thai Industries in Ranong.
He said businesses in Ranong had submitted a letter to Surapong Chainam, an adviser to the foreign minister, calling for the government to urgently settle the problem, but had seen no progress.
Thailand and Myanmar both claim Koh Laem, Koh Kan and Koh Kee Nok at the mouth of the Kraburi River, Mr Nit said.