The Kiwi lost his UFC fight against Brock Lesnar at UFC 200, but it was later found that Lesnar had been doping, and the UFC let him off the hook.

Kiwi MMA fighter Mark Hunt is suing the Ultimate Fighting Championship, its president Dana White, and his former opponent Brock Lesnar for damages "in the millions" of dollars.

The heavyweight fighter filed his civil suit in Nevada District Court on Tuesday, alleging the defendants "affirmatively circumvented and obstructed fair competition for their own benefit", ESPN reported.

It accuses the parties of racketeering, with Hunt seeking financial relief for damages, both physical and to his overall brand.

REY DEL RIO/GETTY IMAGES Mark Hunt takes a shot at Brock Lesnar during the UFC 200 event in Las Vegas, Nevada.

Hunt has been at loggerheads with the UFC since it was revealed former heavyweight champion Lesnar failed multiple drug tests prior to their bout at UFC 200 last July.

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GETTY IMAGES Mark Hunt is suing the UFC organisation and Brock Lesnar.

Lesnar won that fight by decision, but the result was later changed to a no contest once the doping violations were revealed.

The United States Anti-Doping Agency (USADA) handed Lesnar a one-year suspension, while the Nevada State Athletic Commission (NSAC) fined Lesnar US$250,000 (NZ$357,000) - 10 per cent of his US$2.5 million purse - and also suspended him one year.

Both the ban and the financial penalty did not go far enough in Hunt's eyes.

"I want the UFC to understand it's not OK to keep doing what they're doing," Hunt told ESPN.

"They're allowing guys to do this. They had a chance to take all the money from this guy, because he's a cheater, and they didn't.

"What message is that sending to the boys and girls who want to be a fighter someday? The message is, 'You just have to cheat like this and it's OK.' In society, if you commit a crime, you pay. Why is it different in MMA? It's hurt the business, so it's even worse. They need to be held accountable for this."

Hunt's lawyer, Christina Denning, told ESPN on Wednesday (NZ time) that she met with UFC officials prior to filing the lawsuit, but the UFC declined to penalise Lesnar beyond the NSAC sanctions.

"Once we found out the penalty was only 10 per cent of his purse, we went back to the UFC and offered to accept [Lesnar's] purse amount, less than the $250,000 penalty," Denning said.

"We also wanted them to accept the clause moving forward. Mark says the penalties aren't harsh enough. What's interesting is that the penalties are harsh enough on paper, they're just not being enforced by the UFC."

Denning said Hunt is seeking damages "in the millions" in the suit.

Lesnar denies knowingly using any banned substances prior to the fight.

Lesnar was coming out of retirement for the fight, which meant, under the UFC's anti-doping program, he had to undergo four months of random drug testing prior to competing. The UFC exercised its right to waive that rule for Lesnar, citing exceptional circumstances.

The lawsuit alleges that the UFC granted the exemption with "knowledge or willful indifference to the fact that Lesnar was using banned substances", ESPN reported.

Hunt is scheduled to fight Alistair Overeem at UFC 209 on March 5. He had said that he would only take part if his demands around stricter penalties for doping offences were met, but said last week that he was resigned to the UFC not including them in the contract.