Thai police said that they were warned by Moscow that 10 Syrians working for the so-called Islamic State (IS) entered Thailand in October to target Russians.
A leaked Thai police memo says the information was passed by Russia’s intelligence agency. More than 1.5 million Russians visited in 2013.
But Thai police say they have not been able to confirm the presence of these Syrians and officials called for calm.
Russia began air strikes against IS in Syria at the end of September.
An IS-linked group also claimed it brought down the Russian airliner which crashed in Egypt’s Sinai peninsula in October, killing all 224 people on board.