SEOUL (Reuters) - The Korea Olympic Committee has turned down Park Tae-hwan's appeal to overturn a controversial doping suspension, leaving the swimmer's hopes of competing at the Rio Games in the hands of the Court of Arbitration for Sport (CAS).

The former Olympic champion has already served an 18-month ban imposed by swimming's world governing body FINA but is fighting to repeal a KOC regulation that imposed an additional three-year suspension, effectively ruling him out of Rio.

The 26-year-old South Korean lodged a case with CAS but had hoped the KOC might re-consider its hard-line position before going to trial.

The KOC poured cold water on such hopes on Thursday, saying the rule would remain in force.

"The regulation for the selection of national team representatives was made with the aim of demanding a high level of morality of our national team athletes and considering the dignity required of a public figure," the KOC said in a statement carried on South Korean television.

"Doping is against the fair play spirit, a basic requirement of athletes, and we decided that a rigorous response was needed for educational purposes to young athletes."

Park, who won gold in the 400 meters freestyle and silver in the 200 at the 2008 Beijing Games, was left frustrated by the KOC's actions and will be seeking a swift resolution with time running out ahead of the Aug. 5-21 Olympics.

"Park has been trying to work it out with KOC but it ended up only delaying the process," Sean Lim, an attorney with the Lee & Ko law firm representing Park, told a news conference later on Thursday.

"It is a very urgent situation since the deadline to submit final entries for Rio is July 18. We are trying to go through the hearing in June and get decisions from CAS by July 8."

SKIN COMPLAINT

The first Korean to win an Olympic swimming medal, Park's breakthrough in the Beijing pool made him a huge celebrity at home and a magnet for corporate sponsors.

He finished runner-up in both the 200 and 400 at the London Games four years ago but his reputation was shattered when he tested positive for testosterone ahead of the 2014 Asian Games.

Park attributed the failed test to an injection he received at a local clinic, where he said he was being treated for a skin complaint.

Despite the KOC ban, Park entered national swimming trials in April and won all four of his races in times quick enough for Olympic qualification.

CAS has previously struck out double-barrelled punishments for athletes banned for doping-related offences.

In 2011, the Swiss-based tribunal ruled that the International Olympic Committee's 'Osaka Rule', which banned athletes serving suspensions of at least six months from competing at the next Games, violated of its own statutes.

"This is not a matter of winning the medal or not. It is just so heartbreaking to see a young athlete's reputation tarnished for the sake of educating the importance of anti-doping," the swimmer's father, Park In-ho, added.

(Reporting by Jee Heun Kahng; Writing by Ian Ransom; Editing by John O'Brien and Amlan Chakraborty)