By Jon Herskovitz

JOHANNESBURG (Reuters) - A Thai man pleaded guilty on Monday to smuggling rhino horn from South Africa, in a case in which prostitutes posing as big game hunters were used to conceal an international trafficking ring.

Chumlong Lemtongthai is likely to be jailed for more than 10 years under a plea deal that investigators said sealed one of the most important prosecutions in their fight to protect rhinos, whose horns are worth more than gold in parts of Southeast Asia.

Taking advantage of the fact that it is legal for foreigners to hunt rhinos in South Africa and ship horns overseas as trophies, Chumlong hired Thai prostitutes to stage fake hunts.

The women were given about $800 dollars each to go to game farms, take a few shots with small caliber rifles and then pose next to rhinos killed by someone else, according to affidavits presented to the court and seen by Reuters.

"The hunters were a front for our decision to export rhino horn for trade and not for trophies," Chumlong said in a statement to a Johannesburg court.

"I humbly apologize to the court and to the people of South Africa for my role in this matter," he said.

Prosecutors said Chumlong was a major player in a network that included private game reserve owners and a suspected animal parts kingpin in Laos who has built a booming business in rhino horn which sells for $65,000 a kilogram in Asia as medicine.

"The real significance of the guilty plea entered into is that this is the first time the state was able to arrest and prosecute one of the most senior people in an international smuggling syndicate of rhino horn," said Adrian Lackay, spokesman for the South African Revenue Service which investigated the case.

Between October 2010 and May 2011, Chumlong arranged licensed hunts where about two dozen rhinos were killed on the private game reserve of South African Marnus Steyl, according to court documents obtained by Reuters.

In 2011, Chumlong signed an deal with Steyl requesting horns from an additional 50 rhinos, with a street value of about $20 million.

Prosecutors dropped charges against Steyl and other co-accused with the entry of Chumlong's guilty plea.

In the past few years a belief has grown in Southeast Asia - unfounded in science - that rhino horn can be used to prevent and cure cancer.

Increased demand meant poaching has hit record levels in South Africa where, by mid-October, 455 rhinos had been killed illegally - more than 448 during the whole of 2011.

Poaching increased dramatically from about 2007 as a growing affluent class in China, Vietnam and Thailand began spending more on rhino horn.

(Additional reporting by Shafiek Tassiem; Editing by Robin Pomeroy)