By Caroline Stauffer

RIO DE JANEIRO (Reuters) - The Australian swimmer who set off a chain of anti-doping comments at the Olympics says he has no regrets and nothing to apologize for after receiving hundreds of thousands of hate messages on social media.

Mack Horton, 20, called Chinese rival Sun Yang a "drug cheat" before defeating Yang and winning a gold medal in the men's 400 meters freestyle final on Aug 6, inciting the wrath of Chinese social media users.

Yang, who took silver behind Horton, served a three-month ban in 2014 after testing positive for a banned stimulant. He said the stimulant was medication to treat a heart issue and did not enhance his performance.

"I do not think I need to apologize... I just said what is true," Horton told Reuters in an interview on Sunday. "I think people need to be more comfortable talking about doping in sport."

Following Horton's example, American Lilly King wagged her finger at the twice-banned Russian swimmer Yulia Efimova and accused her of cheating before heats on Aug. 8, comments that were later supported by swimming legend Michael Phelps.

"I guess it worked because Lilly King was obviously more comfortable talking about it and so were other athletes," Horton said.

Doping has become a defining issue of the Games, with athletes more outspoken than ever before. The comments have increased tensions between Western athletes and those competing for China and Russia.

"It all get pretty out of control. I had 450,000 hate comments on one of my Instagram photos," Horton said.

Chinese state media called Australia "uncivilized" and "Britain's offshore prison", while the Australian Olympic Committee deleted thousands of vitriolic comments left on Horton's Instagram account.

Efimova, who won the right to compete after winning an appeal against a ban, said there were circumstances when athletes were unknowingly drugged and everyone deserved a second chance.

Horton disagreed.

"The bottom line is what you put in your body is your responsibility, he said. "If you are taking stuff that you do not know what it is, then really it is your fault."

Horton, who hopes to compete in the 2020 Olympics in Tokyo, said he was looking forward to seeing more of Rio and watching other sporting events now that swimming is over.

Not in his plans, however, is a visit to his rival's country.

"Yeah I'm probably not in a hurry to go to China," he said.

(Reporting by Caroline Stauffer; Editing by Brian Homewood)