But the South African said she would "continue her fight for human rights" despite her "disappointment".

Semenya has twice appealed against IAAF rules preventing her from running without medication.

But a ruling allowing her to compete has now been overturned.

Semenya is challenging world governing body the IAAF's new rules that she and other athletes with differences of sexual development (DSD) must either take testosterone-reducing medication in order to compete in track events from 400m to the mile or change to another distance.

Semenya had been able to race while awaiting the decision of a Swiss court, having previously lost an appeal to the Court of Arbitration for Sport (Cas) in May.

The latest ruling by the Swiss Federal Supreme Court means she will not be allowed to compete at the World Championships in Doha.

"I am very disappointed to be kept from defending my hard-earned title," Semenya, 28, said.

"But this will not deter me from continuing my fight for the human rights of all of the female athletes concerned."

The IAAF said it wanted the suspension of the rules to be reversed to avoid "serious confusion" among athletes and event organisers and "to protect the integrity of the sport".

It rejected the accusation in the letter that its regulations "enforce gender inequality", saying in response that the rule was introduced "precisely because the IAAF is committed to protecting the rights and opportunities of female athletes".

In May, Semenya filed an appeal to the court after failing to have new IAAF rules overturned by Cas.

Dorothee Schramm, the lawyer leading Semenya's appeal, added: "The judge's procedural decision has no impact on the appeal itself. We will continue to pursue Caster's appeal and fight for her fundamental human rights. A race is always decided at the finish line."