GENEVA - The ruler of Dubai is being investigated by equestrian authorities after a horse he owns and rides failed doping tests after two races.

Sheik Mohammed said he was unaware of the doping but accepts full responsibility. The drug use came to light following testing by his staff after endurance races this year in Bahrain and Dubai.

The International Equestrian Federation said Tuesday it is investigating. The federation's president is Princess Haya of Jordan, who is married to Sheik Mohammed.

She has led a campaign for a drug-free sport and will step aside from her official duties when the governing body considers the case. Her husband is one of the world's leading breeders and owners of thoroughbred race horses.

The case is likely to go before the federation's seven-man tribunal, which has the power to impose a suspension.

Details of the case were published Tuesday on the federation's Web site. A statement released by the emirate Monday said: "Whilst completely unaware and utterly condemning the administration of these substances, His Highness has volunteered his acceptance that he is legally the person responsible.''

His horse Tahhan tested positive for guanabenz — used to treat hypertension — after competing in 75-mile races at Bahrain in January and Dubai in February.

After the Bahrain race, the horse also had traces of 16b-hydroxy-stanozolol, a metabolite of stanozolol, an anabolic steroid used to build muscle and increase production of oxygen-carrying red blood cells.

It was used legally on 2008 Kentucky Derby winner Big Brown, but also by disgraced Canadian sprinter Ben Johnson during the 100-meter final at the 1988 Seoul Olympics.

Sheik Mohammed had his staff inform the federation when told of the positive cases and instructed his race results be voided, according to the Dubai statement. The federation said Sheik Mohammed waived his right for backup samples to be tested.

Princess Haya was elected federation president in 2006 and became an International Olympic Committee member a year later. Her office said she would defer the presidency during the case to second vice president Chris Hodson and she informed the IOC's ethics commission.

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The 34-year-old princess has campaigned to clean up the sport after six horses failed doping tests at last year's Beijing Games.

She insisted on publicizing the Olympic cases and invited the head of the IOC medical commission to review sport's methods of treating horses and educating riders.

"We feel that we are a clean sport,'' she said in an interview with The Associated Press last week. "Unfortunately the cases we have had have been individually huge in profile. That has left an enormously bad taste among the general public, but it's certainly not reflective of our family. We have paid a very, very high price for actually trying to do the right thing.''

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