Pretoria (AFP) - Star South African 800-metre athlete Caster Semenya said on Friday she hopes to compete in the 200m at the 2020 Tokyo Olympic Games.

The 29-year-old is prohibited from defending her 800m Olympics title because she refuses to adhere to testosterone regulations set by governing body World Athletics.

Semenya, and other female athletes with differences of sexual development (DSD), are banned from competing in races between 400m and the mile unless they take testosterone-lowering medication.

She won the 2012 London and 2016 Rio Olympics 800m titles and was the world champion over the distance in 2009, 2011 and 2017.

The South African must clock a 22.80-second 200m to qualify for Tokyo and her best time, achieved Friday in Pretoria when winning a provincial championships final, is 23.49 sec.

"My dream has always been, and will continue to be, to compete at the highest level of sport," Semenya said on her Instagram account.

"So in order pursue my goals and dreams, I have decided to change events and compete in the 200m.

"This decision has not been an easy one, but I look forward to the challenge, and will work hard, doing all I can to qualify for Tokyo and compete to the best of my ability for South Africa."

Semenya took the athletics world by storm 11 years ago when becoming world champion in Berlin at the age of 19.

But as her list of successes lengthened, rival female athletes began to question how the South African could leave them trailing in her wake.

Semenya is among a minority of female athletes who have an unusually high level of testosterone, which gives them added strength.

The media-shy South African has faced constant legal battles during her career, leading to temporary bans from competing in her favourite 800m.

The latest testosterone regulations left her with a choice of competing in the 200m or a distance longer than the mile.

She has not returned impressive times over longer distances in the past, which prompted her to seek 200m qualification for Tokyo.

Semenya must trim another 0.69 sec off her Pretoria time to secure a place in the South African Olympics team.

The 200m world and Olympic records are held by American Florence Griffith-Joyner, who clocked 21.34 sec at the 1988 Seoul Olympics.

Away from athletics, Semenya joined a Johannesburg-based football club last year but was unable to play immediately because she missed the registration deadline.