Jamaican sprinter Asafa Powell and US 100m record holder Tyson Gay are among a group of athletes who have tested positive for banned substances.
Powell's agent confirmed on Sunday that 100m world record holder Powell and his Jamaican teammate Sherone Simpson had each tested positive for banned stimulants.
Paul Doyle told The Associated Press that they tested positive for the stimulant oxilofrine at the Jamaican championships and were just recently notified.
The news came the same day that American 100-metre record holder Tyson Gay revealed that he also failed a drug test.
Powell helped the Jamaicans to the 400-metre relay gold medal at the 2008 Olympics and was the last man to hold the individual 100 record before countryman Usain Bolt broke it earlier that year.
Simpson won Olympic gold in the women's 400 relay in 2004 and silver in 2012, along with an individual silver in the 100 in 2008.
These doping positives come a month after another Jamaican Olympic champion, Veronica Campbell-Brown, tested positive for a banned diuretic.
Earlier, American 100-metre record holder Tyson Gay said that he had tested positive for a banned substance and said he will pull out of the world championships next month in Moscow and a Monaco meet.
'I was let down'
Gay would not reveal the substance in a phone conversation from Amsterdam on Sunday, but he said he was notified by the US Anti-Doping Agency late last week that a sample came back positive from a May 16 out-of-competition
He said that he would have his "B" sample tested soon, possibly as early as this week.
"I don't have a sabotage story, I don't have any lies," Gay said, as he fought back sobs.
"I don't have anything to say to make this seem like it was a mistake or it was on USADA's hands, someone playing games.
"I don't have any of those stories. I basically put my trust in someone and I was let down."
Asked who that person was, Gay replied: "I can't really say it. Sometimes a human being naturally, generally trusts somebody. That's what people do."
Plagued by ailments
The 2007 triple world champion was healthy again this season after being constantly plagued by hamstring and groin ailments, along with a surgically repaired hip.
He won the 100 and 200 at the US national championships last month, setting up an anticipated showdown with Usain Bolt at the worlds. But that has been scrubbed.
Gay said that he would also pull out of a meet in Monaco and fly back to the headquarters of USADA in Colorado Springs, Colorado, to be on hand when his "B'' sample is tested.
A few years ago, Gay was part of USADA's program called "My Victory", where athletes pledge to compete clean.
Gay said in his testimonial on the website: "I compete clean because I really believe in fairness, and besides that, my mom would kill me! Just being honest."
He has spoken with his teammates, friends and family, including his mother and daughter.
"They already know it is some type of accident, or some type of - I don't want to use certain words, to make it seem like an accident, because I know exactly what went on, but I can't discuss it right now,'' he said. ``My
career and my name have always been better than medals or records or anything like that.
"I've always wanted a clean name with anything. Unfortunately, I have to break this news, that I have a positive 'A' sample."
USATF chief executive Max Siegel said in a written statement that the positive test result was not the news anyone wanted to hear, at any time, about any athlete.
"We do not know the facts of this case and look to USADA to adjudicate it and handle it appropriately," he said.
Gay was tight-lipped on specifics about the case because he said he could not discuss it when asked if what he tested positive for was a steroid.
"I have to go over everything with USADA first," said Gay, who finished fourth at the London Games last summer.
"I will take whatever punishment I get like a man. I do realise and respect what I put in my body and it is my responsibility.
"I'm going to be honest with USADA, about everything, everybody I've been with, every supplement I've ever taken, every company I've ever dealt with,