Khamzat Chimaev’s victory last weekend in a bruising fight served as a declaration in mixed martial arts: Chimaev, an undefeated welterweight, is quickly becoming the Ultimate Fighting Championship’s next superstar.

Yet as his mystique has grown through exciting bouts and promotional spectacle, the same U.F.C. that builds fighters into pay-per-view headliners has sidestepped a problem for Chimaev and others in the sport: the relationships with Ramzan Kadyrov, the strongman leader of Chechnya whose personal businesses have been constrained by the U.S. government.

Hours before his bout on Saturday, Chimaev, 27, posted a picture on his Instagram story that showed him chatting by video with Kadyrov, who has been accused of gruesome human rights abuses and is a close ally of President Vladimir V. Putin of Russia. Chimaev, who was born in Chechnya and moved to Sweden when he was 18, has long been lavished with praise and luxury by Kadyrov, who has hosted him at parties and once gave him a Mercedes-Benz.

In 2017, the U.S. Treasury issued sanctions that blocked U.S. citizens and people present in the United States from doing business with Kadyrov. Several of his associates and some of his businesses were similarly punished in 2020. One of his most visible business pursuits, one that has intertwined repeatedly with the U.F.C. and other combat sports organizations, has been mixed martial arts, including his gym, Akhmat MMA.

The measures against Kadyrov and Akhmat MMA are broad, designed to prohibit “any contribution or provision of funds, goods or services by, to or for the benefit of any blocked person or the receipt of any contribution or provision of funds, goods or services from any such person,” according to the Treasury’s Office of Foreign Assets Control.

Chimaev’s picture on Saturday included a caption with the phrase “Akhmat Sila,” a battle cry popular among Kadyrov loyalists that translates to “Akhmat Power.” Akhmat is a variation of the name of Kadyrov’s father, which Kadyrov uses in numerous ways in Chechnya to brand businesses, streets and other things.

Chimaev’s manager and agent did not respond to messages requesting comment.

Kadyrov has many ties to combat sports athletes.

Numerous athletes and others in the world of mixed martial arts have ties to Kadyrov, who has supplied Chechen soldiers to support the Russian forces fighting in Ukraine. He has been one of the most fervent supporters of the war and has pushed for taking control of Kyiv, Ukraine’s capital. In one of his recent addresses, Kadyrov said that Chechen soldiers would first “liberate” Donetsk and Luhansk, “and then we will take Kyiv next.”

Before the war, he was accused of brutal human rights abuses, including kidnapping, torturing and killing L.G.B.T.Q. people in Chechnya.

Athletes training with his Akhmat MMA gym have fought regularly in U.F.C. bouts for years. American fighters have traveled to Chechnya, visiting Kadyrov and interacting with his athletes. Some American fighters have even fought in Kadyrov’s fighting league, Absolute Championship Akhmat.

And after the U.S. Treasury’s guidance and Russia’s invasion of Ukraine, little changed, although Kadyrov’s most visible displays with fighting celebrities have slowed.

“There are a number of people involved in an M.M.A. fight, any of whom could be in violation if they are providing or receiving goods, services or funds from Akhmat,” said Shahroo Yazdani, a lawyer at Price Benowitz who specializes in sanctions cases.

In a statement to The New York Times, the U.F.C. said it had “no contractual relationship or any commercial dealings with Ramzan Kadyrov or any of his family, associates or affiliated companies that have been designated by the U.S. Department of the Treasury’s Office of Foreign Assets Control.”

The U.F.C. said that its fighters were independent contractors and that it entered into contracts with them directly, without intermediaries. The organization also said it had no affiliation with Akhmat MMA and that it was in compliance with all laws and regulations. (The Times first asked the U.F.C., which is owned by the sports and entertainment conglomerate Endeavor, about Kadyrov in 2021. The U.F.C. reiterated its written statement when asked about him after Russia invaded Ukraine and again this week after Chimaev’s fight.)

Details are often murky about how mixed martial arts fighters are paid, since their contracts with organizations like the U.F.C. are usually private. In general, fighters are responsible for arranging their own training and promotion through agents, managers and coaches. The sanctions put pressure on these arrangements while raising wider questions about how they are applied, especially to people who are not American citizens and who often fight outside the United States.

“Treasury is aware of Kadyrov’s ongoing interest in M.M.A. and will continue to take action as appropriate,” a spokeswoman for the Treasury Department said in a statement.

The U.F.C. has long cultivated a brash, rebellious image, embracing the brutality of combat sports, pushing the boundaries of propriety and the law and eschewing much of the button-down visage displayed by other major sports leagues.

Since Russia’s invasion, major sports leagues worldwide have distanced themselves from Russian owners, teams and athletes, while the U.F.C. has maintained its broadcast partnership with a Russian state-controlled media company and prominently featured Russian athletes in its events.

But the ties to Kadyrov in mixed martial arts are different from what other sports have had to confront.

Chimaev was once represented by Ali Abdelaziz, a manager. He is one of the most powerful figures in mixed martial arts and has had numerous ties to fighters who have trained or appeared at Akhmat MMA. Abdelaziz, 44, a U.S. resident who was born in Egypt, represents four of the five fighters affiliated with Akhmat MMA on the U.F.C. roster. At least seven other fighters managed by Abdelaziz, including the current U.F.C. welterweight champion, Kamaru Usman, have visited Kadyrov’s M.M.A. gym in Russia.

Abdelaziz did not respond to messages seeking comment, but he has said in the past that he doubts that Kadyrov committed human rights violations, stating that he “doesn’t believe anything the media says.”

Kadyrov has called Chimaev his favorite fighter and once boasted that he persuaded Chimaev not to retire after a serious case of Covid-19. Last year, Chimaev was present when Kadyrov issued a death threat to a 15-year-old Chechen teenager who had spoken out against his regime.

“You won’t sleep at night. You’ll be writing your will,” Kadyrov said during a live Instagram stream aimed at the teenage dissident. “I will destroy you.”

‘I want to say hello to my country.’

After his victory against Gilbert Burns on Saturday in a bout that many observers praised as the best U.F.C. fight so far in 2022, Chimaev grabbed a microphone from the commentator Joe Rogan after an interview and said, “I want to say hello to my country.” He then spoke in Chechen.

“Brother, I know you’re watching from home,” Chimaev said. “I said that today I would finish quickly, but today it did not work out. Thank you, brother. God bless you. I know you’re watching this fight. Thanks to all Chechens. God bless you.”

It is not explicitly clear whom Chimaev was referring to. Chechens, including Kadyrov, often use the word “brother” as a term of respect for people who are not their direct siblings. Chimaev also has an older brother, Artur.

The Chechen word is “vasha.” Kadyrov has addressed Chimaev with it, and Chimaev addressed Kadyrov directly with it after the fight in a comment on Instagram. “Thank you brother. God bless you. Akhmat is power. Chief Champion,” Chimaev said.

Whomever Chimaev was referring to during the U.F.C. broadcast, the fight and the in-ring interview were not seen by mixed martial arts fans in Poland. Polsat, which showed the rest of the U.F.C. 273 card, declined to broadcast the fight between Chimaev and Burns because of Chimaev’s post showing his video chat with Kadyrov.

“This is a clear signal of mutual support, and with Ukraine under attack from Russia, the post is simply provocative,” Polsat said in a statement.

The Treasury sanctions have created confusion in the M.M.A. world.

The Treasury Department does not make public the vast majority of enforcement actions it takes, but Jamal El-Hindi, a lawyer at Clifford Chance who spent two decades at the Treasury Department, said the sanctions against Kadyrov and his businesses were far-reaching. They prohibit U.S. citizens and green card holders, as well as anybody on U.S. soil, from interacting with Kadyrov and his businesses.

El-Hindi and other lawyers said sanctions and their enforcement were broad, flexible and opaque precisely because they were designed to be primarily a foreign policy tool.

“The purpose of sanctions is to affect foreign policy and have impact,” El-Hindi said. “To the extent that an enforcement action against somebody who violated sanctions will aid in the foreign policy goal, that is the driver for doing the enforcement.”

Before the latest restrictions, in December 2020, dozens of U.F.C. fighters and combat sports celebrities visited Akhmat MMA facilities and attended fights alongside Kadyrov at his invitation. His previous guests included celebrities like the actor Steven Seagal and the boxer Floyd Mayweather Jr., and former U.F.C. champions like Frank Mir and Khabib Nurmagomedov.

Over the past 15 months, however, there has been a slow, sporadic retreating of Akhmat MMA from the combat sports world in the United States. Fewer fighters have been publicly photographed at Akhmat gyms. YouTube pulled down Akhmat MMA’s page last year, saying it had done so because of “compliance actions.” Meta, the parent company of Facebook and Instagram, suspended Akhmat MMA’s Facebook and Instagram pages after The Times inquired about them in March.

One of the notable exceptions is Usman, who was shown in an Instagram video alongside Kadyrov’s teenage son at the boy’s birthday party in November 2021 — nearly a year after the Treasury Department cracked down on Kadyrov’s fight club. During a previous visit to Akhmat MMA, in November 2020, Usman sparred with the boy and took a picture wearing a sweater with the gym’s slogan, “Akhmat Sila.”

Usman did not respond to a message seeking comment sent to his manager, Abdelaziz.

The lack of clarity over the interpretation and enforcement of the Treasury rules has led to confusion in the mixed martial arts world.

Brett Cooper, an American journeyman mixed martial artist who is scheduled to fight in the Professional Fighters League in May, learned about the December 2020 sanctions against Absolute Championship Akhmat when he landed in Russia days before a scheduled fight that month. After his manager spoke to a lawyer, Cooper pulled out because he believed he could be prosecuted for receiving money from an organization owned by Kadyrov.

But Cooper now says he believes he got bad advice and should have fought. “I was cutting weight and probably didn’t make the most clearheaded decision,” he wrote in an email. “In hindsight I should have just competed anyway.”

According to Mansur Sadulaev, the founder of Vayfond, a Chechen human rights organization in Sweden, Kadyrov becomes close to athletes by showering them with luxury cars and homes, then uses them for propaganda.

Kadyrov has long used sports, particularly his combat sports businesses, to rub shoulders with fighters and present himself as a benevolent, sports-loving leader rather than an autocrat with a long record of human rights abuses.

“All these athletes are direct accomplices of Kadyrov’s cruel crimes,” Sadulaev said in an email.

Kadyrov’s ownership of Akhmat MMA allows him to go far beyond merely associating with athletes. He uses it to express Chechen machismo and has directly tied mixed martial arts to his military forces. Some fighters who train at Akhmat MMA also moonlight as soldiers, blurring lines between athleticism and militarism.

Mohsen Zarkesh, a lawyer who specializes in Treasury sanctions, said the circumstances “are definitely problematic, not just for the U.F.C. but also the entire M.M.A. world.”

Kasia Pilat contributed reporting.