The world of athletics has been rocked after a number of high-profile sprinters admitted to having failed drug tests, including former world record holder Asafa Powell of Jamaica and American Tyson Gay.

Powell’s agent Paul Doyle confirmed that the former 100 metres world record holder had tested positive for a banned substance.

Powell, 30, has won gold medals in the 4x100m relay at the Olympics and World Championships and held the world record before his compatriot Usain Bolt.

Powell has run 9.88 seconds this year, but failed to make the Jamaican team for next month’s World Championships.

He is one of a reported five Jamaicans to have tested positive, but they do not include Bolt, who is in a different training group.

Bolt’s agent Ricky Simms said: “I was just with him in Jamaica and we’ve had no information and we’ve not been contacted by anyone. It is not anyone that I’m connected with.”

Powell ran his world record of 9.72sec in 2008 and has often failed to live up to expectations on the biggest stage.

Double sprint world champion Gay said on Sunday he had tested positive for a substance he could not identify and was pulling out of the World Championships in Moscow.

Gay, who had the year’s fastest 100 metres time of 9.75 seconds, told two reporters in a telephone conference call he was notified by the US Anti-Doping Agency (Usada) on Friday that his A sample from an out-of-competition test on May 16th had returned a positive.

“I don’t have a sabotage story. I don’t have lies...I basically put my trust in someone and I was let down,” said Gay, who added he had never knowingly taken a performance-enhancing drug.

“I made a mistake,” added the 30-year-old sprinter from his training base in Amsterdam.

"I am pulling out of Monaco (Diamond League meeting on Friday) and the world championships."

Gay, the world 100 and 200 champion in 2007, said he could not divulge the substance or how the positive occurred.

“I am not allowed to talk about those things right now. I know exactly what went on, but I can’t discuss it right now,” he added.

“I hope I am able to run again,” Gay said. “But I will take whatever punishment I get like a man.”

Usada said in a statement: “In response to Mr Gay’s statements, Usada appreciates his approach to handling this situation and his choice to voluntarily remove himself from competition while the full facts surrounding his test are evaluated.

“The B sample will be processed shortly, and as in all cases all athletes are innocent unless or until proven otherwise through the established legal process, and any attempt to sensationalise or speculate is a disservice to due process, fair play, and to those who love clean sport.”

Healthy after years of injury, Gay, the joint second-fastest man in history over 100 metres, had been considered a strong challenger for Jamaican world record holder Usain Bolt at the August 10th-18th world championships after winning the American trials in blazing times.

He had put down the year’s three fastest 100 times, topped by his 9.75 at last month’s US meeting. Only Bolt has run faster than Gay’s 19.74 seconds in the 200 this year.

“It has been tough for me,” said the soft-spoken Gay. “I have always been a drug-free athlete.”

Following his 2007 victories, Gay appeared set to win his first Olympic individual gold medal at the 2008 Beijing Games but the emergence of Bolt and injuries ended that chance.

In 2009, he ran an American record 9.69 seconds, at the time the second fastest ever, but was never fully healthy at ensuing Olympic and world championships.

He finished a heart-breaking fourth at the 2012 London Olympics but won a silver medal in the 4x100 metres relay.

USA Track & Field said in a statement: “It is not the news anyone wanted to hear, at any time, about any athlete.

“As we approach the world championships, we will remain focused on the competition at hand and winning the right way.”

The governing body said it did not know the facts of the case and looked to the sport’s governing body, to adjudicate it and handle it appropriately.

Jamaican Olympic relay silver medallist Sherone Simpson admitted she had tested positive for a stimulant at last month’s national championships.

Simpson, 28, was a member of the Jamaican team that finished second in the 4x100 relay at last year’s London Olympics.

She finished equal second in the 100 metres at the 2008 Beijing Games and won a gold medal in the 4x100 relay four years earlier in Athens.

“This is a very difficult time for me,” Simpson said in a statement.

“I was notified on July 14, 2013 that my urine sample taken at the National Senior Championship, June 21, 2013 after the 100m finals returned a positive analytical finding for a stimulant, oxilofrine (methylsynephrine).

“As an athlete, I know I am responsible for whatever that goes into my body. I would not intentionally take an illegal substance of any form into my system.”