Australian swimmer and Olympic gold medalist Mack Horton on Monday refused to share a podium with Chinese rival Sun Yang, whom Horton has long accused of being a "drug cheat."

Horton, 23, did not take the medal stand nor acknowledge Sun after they finished second and first, respectively, in the 400-meter freestyle at the 2019 World Aquatics Championships in South Korea.

"Frustration is probably it," Horton told reporters after the race. "I think you know in what respect."

Sun, a 10-time world champion and three-time Olympic gold medalist, was suspended for three months in 2014 after taking a banned heart medication. More recently, he has been accused of smashing a vial of his blood with a hammer after drug-testers collected samples at his home in September, according to multiplemediareports.

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When asked about Horton's actions on the podium, Sun toldreporters that "disrespecting me is OK, but disrespecting China was very unfortunate and I felt sorry about that."

The International Swimming Federation, FINA, said in a statement that it planned to send a warning letter to Horton and Australia's swimming federation, urging the swimmer to "not use FINA events to make personal statements or gestures."

"While FINA respects the principle of freedom of speech, it has to be conducted in the right context," the federation said in the statement.

Sun has denied wrongdoing in the September incident and was cleared by FINA's doping tribunal. The World Anti-Doping Agency has appealed FINA's ruling, and Sun has asked for the Court of Arbitration for Sport to grant him a public trial in September to issue a final decision on the matter ahead of the 2020 Olympic Games in Tokyo.

Contributing: The Associated Press

Contact Tom Schad at tschad@usatoday.com or on Twitter @Tom_Schad.