Two-time Olympian Mara Yamauchi has voiced her displeasure after a transgender athlete beat thousands of women in the female category of the London Marathon.

Yamauchi finished in sixth place in the marathon at the Beijing Olympics in 2008 while representing her home country of Great Britain. Yamauchi did not mince words when she spoke on transgender racer Glenique Frank's win at the marathon over the weekend.

"Males in the [female] category is UNFAIR for females," Yamauchi wrote in a tweet.

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Mara Yamauchi finishes a race

Mara Yamauchi of Great Britain finishes 10th during the Virgin London Marathon on April 25, 2010, in London. (Christopher Lee / Getty Images)

"Nearly 14,000 actual females suffered a worse finish position [because] of him," Yamauchi wrote on Twitter.

She also estimated that during her time as the second-ranked woman in the world "at least 1,300 men ran faster than me."

Yamauchi noted that United Kingdom Athletics applied World Athletics' rules on the exclusion of transgender women from elite female competitions. She said this practice made it "fair for athletes who have gone through male puberty to be excluded from the female category in athletics."

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On the other hand, the rules permitted athletes who had already entered events to still run in certain categories, even if it was not in their biological sex.

"This male competed under U.K. Athletics’ transitional arrangements, but it is still wrong and unfair," Yamauchi told Telegraph Sport.

Mara Yamauchi speaks at an event

Two-time Olympian Mara Yamauchi has voiced her displeasure after a transgender athlete beat thousands of women in the female category of the London Marathon. (Ulrich Roth / Getty Images / File)

Frank previously ran at an event in New York City while wearing a bra and a wig.

Frank, who is a British citizen, identifies a female.

"I ticked female because I see myself as female," said Frank, who came out a few years ago as Glenique, adding that it was "since I was 5 that I was in the wrong body."

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Frank, who works as a personal trainer, also noted that the public backlash has been "traumatic."

Still, "I get it," Frank said of the criticism. "I feel sad that I’ve upset Mara because I respect her."

Mara Yamauch during a elite racing event

Mara Yamauchi of Great Britain estimated that during her time as the second-ranked woman in the world "at least 1,300 men ran faster than me." (Jed Leicester / Getty Images / File)

After running a 17th career marathon, Frank excitedly spoke about using "girl power" to help get through the race.

Some of Frank's older social media posts show photos of a man who was married at the time.

During this past weekend's race, Frank gushed about soon becoming a "gran."

"So I’m going to be a gran — Granny G!" Frank said in reference to the expectation of becoming a grandparent.

Frank said she was shocked at the backlash given that she was not an elite runner competing for prize money or a place on the podium. Instead, she’s raised the equivalent of $37,000 for charity in the races.

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Going forward, Frank plans on entering races "under 'other' or 'male'" categories.

"And I’ll still do [the race] in four hours and I won’t steal anybody’s money," Frank said.