(CNN) Australian swimmer Mack Horton has reignited his feud with Chinese swimming star Sun Yang -- and most of China -- by refusing to share the podium with his longtime rival.

Horton came second to Sun in the 400-meter freestyle event at the 2019 World Aquatic Championships in South Korea on Sunday, then refused to acknowledge his Chinese competitor, who he has previously called a "drug cheat."

Sun received a three-month ban after testing positive for a banned substance in 2014, and is facing renewed allegations according to ABC

"I just won't share a podium with someone that behaves in the way that he has," Horton said after the race. When asked how he felt, the 23-year-old Australian summed it up as "frustration," the ABC reported

According to Chinese state media CGTN, Sun responded to Horton's actions, saying : "You could choose not to respect me, but you must respect China."

On Monday, the competition organizers said they had decided to send a warning letter to both Horton and the sport's national governing body, Swimming Australia.

"While FINA respects the principle of freedom of speech, it has to be conducted in the right context," the organizers said in a statement, adding that athletes were not to use the events to make personal statements or gestures.

But Swimming Australia's CEO Leigh Russell stood by Horton, saying in a statement sent to CNN: "Swimming Australia respects the position Mack Horton took during the medal ceremony and understands his sense of frustration."

Silver medalist Mack Horton of Australia and gold medalist Sun Yang of China pose during the medal ceremony for Men's 400m Freestyle Final on day one of the Gwangju 2019 FINA World Championships at Nambu International Aquatics Centre on July 21, 2019 in Gwangju, South Korea.

-- who are both -- have a long, bitter rivalry. The pairwho are both competing Tuesday in the 800m freestyle heatshave a long, bitter rivalry.

Before the 400m freestyle race at the 2016 Olympics in Rio de Janeiro, Brazil, Horton said his rival was a " drug cheat ."

After the race, Horton described his win as "one for the good guys." Sun broke down in tears surrounded by Chinese media after his defeat, while the Chinese swim team manager Xu Qi demanded an apology

Australia's chef de mission Kitty Chiller said Horton had every right to express his views -- and the team had no intention of making an apology.

2016 comments went viral in China, where many believed he had deliberately tried to psych out Sun. Horton's Instagram page was bombarded with derogatory messages, and an Horton's2016 comments went viral in China, where many believed he had deliberately tried to psych out Sun. Horton's Instagram page was bombarded with derogatory messages, and an op-ed published by the nationalistic tabloid Global Times described Australia as a country "at the fringes of civilization" and referred to its history as "Britain's offshore prison."

Taking a stand or disrespecting China?

Once again, Horton's Instagram posts have become the target of pro-China users, who left comments such as "You don't deserve to shake Sun's hand" and "You will lose forever."

The issue was also one of the top trending topics on Chinese microblogging site Weibo on Monday -- although Chinese media did not mention the drugs context, and used a picture that made it appear that Horton was kneeling at Sun's side.

"Horton is a man with a small heart," wrote one person on Weibo. "Being this dramatic because of his bad performance -- Sun Yang should stay away from this kind of toxic rubbish," said another.

Silver medalist Sun Yang of China, gold medal medalist Mack Horton of Australia and bronze medalist Gabriele Detti of Italy pose during the medal ceremony for the Final of the Men's 400m Freestyle on Day one of the Rio 2016 Olympic Games at the Olympic Aquatics Stadium on August 6, 2016 in Rio de Janeiro, Brazil.

The response was very different in Australia, where fellow swimmers praised Horton's stance.

In an Instagram story, Australian Olympic medal-winning swimmer Cat Campbell called Horton a "legend." "Taking a stand for clean sport," she captioned a photo of Horton standing to the side of the podium. "Mack Horton, we salute you."

David McKeon, another Australian Olympian, tweeted : "Absolutely awesome to see Mack Horton protesting clean sport by not getting up on the podium next to Sun Yang."

Sun is not the first Chinese swimmer to be accused of doping. In 2012, then 16-year-old swimmer Ye Shiwen won gold at the Olympics and set a new world record, prompting allegations of doping . International Olympics Committee spokesman Mark Adams called doping allegations against Ye "sad" and "pure rumor."

At the time, the head of China's swimming team, Xu Qi, noted that similar allegations hadn't dogged other top swimmers in recent years.

"Ian Thorpe was called a genius, Michael Phelps got eight gold medals in Beijing. Ryan Lochte, Missy Franklin are both recognized as geniuses. There were geniuses in France and South Africa. We admit and accept these geniuses, but why can't a genius come from China, a country with a large population?"