There was no border clash between armed Thai men and Myanmar soldiers on Friday as reported by some media, Foreign Minister Surapong Tovichakchaikul said on Saturday.
It was just a misunderstanding by Myanmar authority, he added.
There was a bushfire in the area when the 13 Myanmar soldiers, who lost their way in the forest, were calling for help from other patrol units through telecommunication radio, Mr Surapong said.
Cracking sound from the forest fire, similar to those of gun shots, had caused other military troops hearing the SOS call to understand that the soldiers were being attacked and finally killed, he said.
Citing a security source, local media on Friday reported that a group said to be forest encroachers killed 13 Myanmar soldiers at the border opposite Ranong.
The source said the attackers exchanged gunfire with the soldiers patrolling along the border at Ban Inthanin Kwang in Kawthaung province in southern Myanmar, opposite Kra Buri district of Ranong.
Two soldiers were still missing, the source added.