Gennady Golovkin says he received photos from doctors showing that Canelo Alvarez was taking pills and "absolutely" still wants the rematch on May 5. (2:05)

Six weeks before unified middleweight world champion Gennady Golovkin and Canelo Alvarez are due to meet in a highly anticipated rematch, Golovkin has accused his rival of being a serial drug cheat.

Alvarez tested positive for the banned performance-enhancing drug clenbuterol in random urine tests conducted by the Voluntary Anti-Doping Association in his hometown of Guadalajara, Mexico, on Feb. 17 and Feb. 20.

Speaking on Tuesday to a group of reporters at his training camp in Big Bear Lake, California, Golovkin said he didn't believe Alvarez's explanation for the positive test, which was that he ate contaminated beef. That has been an ongoing problem for athletes from Mexico, where farmers include the substance clenbuterol, which is prohibited in the United States, in cattle feed because it helps reduce fat and increase lean muscle mass.

"Again with Mexican meat? Come on," Golovkin said. "I told you, it's not Mexican meat. This is Canelo. This is his team. This is his promotion. Canelo is cheating. They're using these drugs, and everybody is just trying to pretend it's not happening.

"This guy, he knows. This is not his first day in boxing. He proves he gets benefits from everyone and he can get away with it. Check him on a lie detector and then we can find out everything."

Speaking by phone to ESPN later Tuesday, Golovkin added: "I think it is silly to blame the meat because an athlete at this level should not be caught on the meat. I eat Mexican food all the time and I've never had that problem."

Golovkin (37-0-1, 33 KOs) and Alvarez (49-1-2, 34 KOs) are set for a rematch on May 5 (HBO PPV, 8 p.m. ET) at the T-Mobile Arena in Las Vegas, where they put on an action-packed fight on Sept. 16 that many thought Golovkin won but that was ruled a draw.

Because of the positive tests, Alvarez is now subject to more rigorous testing. The Nevada State Athletic Commission has declined to comment or announce any disciplinary action while it is in the process of investigating the situation.

For now, the fight remains on.

Golovkin told reporters he thought that the recent positive test is not indicative of the first time Alvarez has used performance-enhancing drugs. Golovkin said he thought Golden Boy Promotions CEO Oscar De La Hoya, Alvarez's promoter and an International Boxing Hall of Famer who won world titles in six weight classes, is "dirty," as well.

"It was pretty obvious when [Alvarez's] muscles were all [enlarged] ... and with the traces of injections, which were visible," Golovkin said. "Before the first fight, I knew he was not clean. I can talk about Oscar De La Hoya too. He is also not clean. He's dirty."

Gennady Golovkin, left, and Canelo Alvarez fought to a draw in their September 2017 bout. Ethan Miller/Getty Images

Golovkin's comments about injection marks stem from the fact that he and his promoter, Tom Loeffler, said they have been sent videos and photos of Alvarez apparently taking some kind of pill following the weigh-in for the fight in September, in addition to photos that show him having apparent injection marks on his abdomen.

"People were sending him videos and photos, and they said he should ask the commission what these photos and videos are," Loeffler told ESPN. "People were telling him to get the commission to clarify what it was. But he doesn't think Canelo was smart."

Golovkin told ESPN that as long as the commission allows the fight to go on, he will get in the ring "and do my job."

"If nobody from the commission will cancel it, I will do my job," Golovkin said. "But this is a very hot topic about doping. What did he inject in his belly? What are the marks on his belly? Look at the photos. These questions should be asked of the commission."

Golden Boy Promotions president Eric Gomez has noted that Alvarez tested negative for any banned substances three times, on March 3, 5 and 9, since the positive test. He also told ESPN that Alvarez has had more recent tests but the results have not yet come back. Gomez also took exception to Golovkin's accusations.

"[Golovkin] doesn't sound like a confident fighter. It sounds like he wants to try to find a way out of the fight," Gomez told ESPN after being told about Golovkin's comments. "If that's what he wants, he should just say so. Just last week he said the opposite. The remarks about the needle marks, the remarks about Oscar, the defamatory things he said, we'll deal with them appropriately.

"As far as Canelo, he is training hard for the fight. He didn't need motivation for this fight, but now he's got added motivation. There's an ongoing investigation, and when it's completed, you'll hear from Canelo."

Alvarez's only public comment on the situation came in a statement Golden Boy released from him on the day the positive test results were revealed earlier this month.

"I am an athlete who respects the sport and this surprises me and bothers me because it had never happened to me," Alvarez said. "I will submit to all the tests that require me to clarify this embarrassing situation, and I trust that at the end the truth will prevail."