The southern army chief has warned people living along the border not to cross illegally into Malaysia, because authorities there are enforcing strict controls.
Many local people cross back and forth to see relatives or conduct business, using piers on the Golok river and avoiding legal channels. Some Thai students go to nearby schools in Malaysia and some Malaysians make brief visits to enjoy the nightlife.
Fourth Army Region chief Lt Gen Paisan Nusang said residents of Sungai Kolok district in Narawthiwat province risk detention and legal action if they illegally cross the river, which marks the frontier, into Malaysia's adjoining Kelantan state.
"Some Thai citizens have been detained by Malaysian authorities for crossing the border using illegal routes in Sungai Kolok," Malaysia's Bernama news agency quoted him as saying on Sunday.
The southern army chief issued the warning in response to questions from Malaysian reporters visiting Songkhla province on Saturday, the report said.
It was the first time he has reacted to Malaysia's decision to take serious action against people illegally entering Kelantan from Narathiwat to combat smuggling and other border crime. Malaysian authorities sometimes refer to the illegal crossings as "rat routes".
Lt Gen Paisan called the Malaysian move a "positive and appropriate step" to control the border, even though it could have an impact on tourism.