Caster Semenya reacts after winning the gold medal in the 800m at the 2017 IAAF World Championships in London. Photo: REUTERS/Toby Melville

LAUSANNE, Switzerland - The Court of Arbitration for Sport (CAS) said Tuesday it had opened a probe into Caster Semenya's challenge of controversial new IAAF rules on testosterone occurring in female athletes.

CAS said it had "registered a request for arbitration" filed by the South African two-time Olympic gold medallist against the "International Association of Athletics Federations' (IAAF) 'Eligibility Regulations for Female Classification (Athletes with Differences of Sex Development)' that are due to come into effect on 1 November 2018".

PREVIOUSLY: Semenya starts legal battle against IAAF: 'I am a woman and I am fast'

Semenya, CAS said, sought a "ruling from CAS to declare such regulations unlawful and to prevent them from being brought into force. An arbitration procedure has been opened". The IAAF announced its new rules targeting women who naturally produce unusually high levels of testosterone in April, arguing that hyper-androgynous competitors enjoy an unfair advantage.

Athletes classified as "hyper-androgynous", like Semenya, will have to chemically lower their testosterone levels to 5 nanomoles per litre of blood to be eligible to run any international race of 400 metres up to the mile. Semenya, who has undergone several sex tests since her first title in 2009, has called the rules discriminatory and violate the IAAF's Constitution and the Olympic Charter.

The 27-year-old has been at the centre of debate because of her powerful physique, one of the effects of hyper-androgenism which causes those affected to produce high levels of male sex hormones.

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