In a leaked police document, the Russian Federal Security Service alerted the Thai authorities about the presence of the Syrians who travelled to many cities including Pattaya and Phuket.
Deputy spokesman Pol Maj Gen Songpon Wattanachai confirmed the document was real.
In the document, Special Branch police urged an intensification of security around "target areas that Russian authorities are concerned about" including venues associated with allies that have taken part in attacks on Islamic State in Syria.
Russia began air strikes in Syria on Sept. 30 and hasstepped up attacks in recent weeks. An Islamic State affiliateclaimed responsibility for downing a Russian airliner over Egyptin October, killing all 224 people on board.
Two senior police officers told Reuters that the Special Branch, which deals with national security issues, circulated the document to other police units.
According to the document dated Nov 27, the Russian intelligence agency warned Special Branch police that the Syrians entered Thailand between Oct 15 and Oct 31. The document was circulating on social media on Thursday.
"The document is real. We received it from Special Branch," said one of the police officers, who handles international crime matters. He declined to be identified because of the sensitivityof the matter.
"I have to deal with this issue now," he said. "The original communication was by word of mouth between Russian and Thaipolice. I don't know how the document leaked."