PARIS -- In the wake of a Chinese doping scandal, Michael Phelps doubled down Monday on his support for tougher sanctions -- including a lifetime ban for anyone who tests positive for a banned substance.

"If you test positive, you should never be allowed to come back and compete again, cut and dry," Phelps said. "I believe one and done."

The World Anti-Doping Agency and World Aquatics have acknowledged that 23 Chinese swimmers tested positive for a banned substance ahead of the Tokyo Olympics. The results were not made public until media reports surfaced this year, with both bodies accepting the Chinese explanation that the positive tests were caused by tainted food.

Nine of those swimmers won medals -- several as part of relay teams -- in Paris, leading British star Adam Peaty to complain that the playing field was not even.

Phelps reiterated those sentiments, saying the Chinese swimmers who tested positive should not have been allowed to compete in either Tokyo or Paris -- or anywhere else, for that matter.

"If everybody is not going through that same testing, I have a serious problem because it means the level of sport is not fair and it's not even," he said. "If you're taking that risk, then you don't belong in here."

When Phelps was setting multiple world records and becoming the most decorated Olympian ever, he knew there were plenty of people who scrutinized his performances, wondering if he could be pulling off such amazing feats without a pharmaceutical boost.

Phelps said he actually subjected himself to extra testing in the leadup to the 2008 Beijing Olympics -- where he broke Mark Spitz's iconic record with eight gold medals -- to alleviate any doubts he was racing clean.

"People called me a cheater throughout my career," he said during a wide-ranging media availability put on by one of his sponsors, Omega. "I subjected myself to do more testing -- blood and urine -- weekly. Why? For the reason that I could say I'm not cheating, and I am clean and here are the results.

"I did it the clean way," he added. "I won 23 Olympic gold medals the clean way. It can be done."

Phelps said he always felt like some competitors were doping during his five Olympics, in which he won 28 medals overall.

"I don't think I ever competed in an even playing field or a clean field," he said. "I have some speculations of some athletes that I competed against that I thought they were [doping]. But that's out of my control."

Since retiring from the sport after the 2016 Rio de Janeiro Games, Phelps became more outspoken about issues such as mental health and anti-doping efforts. He recently testified before the U.S. Congress on the latter issue, calling for major reforms to a system that many people believe is broken.

"What has to happen is everybody has to come together and figure out one way to test everybody all over the world. Period," Phelps said. "And if you test positive, you should never be allowed to come back and compete again."

He said he understands the frustration of athletes such as Peaty, whose British team finished fourth in the men's 4x100-meter freestyle relay Sunday -- a race won by the Chinese.

"It does break my heart to see people put hard effort into four straight years to prepare for an Olympic Games, then to have it taken away from them by somebody who is cheating," Phelps said. "It's not right. I stand for that and I will always stand for that."

He has a suggestion for athletes who want to dodge the rules.

"Go ahead and go to the cheater games," he said. "Keep the Olympics about integrity."