Thai police have arrested 10 Russians who allegedly organised sexual training courses for their compatriots in the seaside resort city of Pattaya.

Police said 33 Russian tourists in total attended the class held at a hotel. But only 10 "instructors" were arrested late Sunday on immigration charges, including working without a permit.

"The hotel management said they had no details on the event but they booked it for a seminar and training," Pattaya tourist police official Piyapong Ensarn told AFP.

"Some participants told police that they had to pay 20,000 baht ($640) but some said they attended for free."

One of the suspects was identified as Alexander Kirilov, 38, whom police described as an organiser.

Police also found white t-shirts with the words "sex animator" and certificates intended for those who took part in the course.

Pattaya, located just two hours from Bangkok, emerged as a raucous party destination during the Vietnam War when it attracted American GIs on leave.

Its sex tourist industry thrives despite prostitution being illegal in Thailand and occasional crackdowns on the trade.

But Thailand remains sensitive to its seedy reputation.

On Tuesday officials said they had sent a letter to the government of Gambia after an official there reportedly described the kingdom as a destination for sex tourists.