Nine track and field athletes have been suspended from the Olympics for doping offences, the International Association of Athletics Federations has announced.
Morocco's Mariem Selsouli - one of the favourites for the women's 1500m - is out of the London Games, as well as leading men's marathon runner Abderrahim Goumri.
Selsouli gave a sample which contained a banned diuretic shortly after running the fastest 1500m time this year of 3min 56.15s in Paris earlier in July. The 28-year-old has become one of more than 100 athletes worldwide who have been caught in the past six months.
The anti-doping operation at this year's Olympics will be the most rigorous in history, the BBC reports. There are new ways to detect banned substances like human growth hormone and synthetic testosterone, which have previously dipped beneath the radar.
All the athletes were caught with the aid of the Athlete Biological Passport programme, which is being used for the first time in London.
Meanwhile, David Howman, the New Zealander at the head of the World Anti-Doping Agency, says they are determined to crack down on any drug-taking athletes at the Games.
Triple jumper withdrawn over tweet
Greek triple jumper Paraskevi Papachristou has been withdrawn from the Olympics after causing an uproar at home for an apparently racist comment on social media site Twitter.
"With so many Africans in Greece... the West Nile mosquitoes will at least eat homemade food!!!" she posted on her Twitter account.
Greek's Olympic Committee says she was being pulled from the team because her comments were against the Olympic spirit, Reuters reports.
The 23-year-old athlete, who was scheduled to leave for her first Olympics next week, later apologised for what she says was "an unfortunate and tasteless joke".
One man has died in a small outbreak of the West Nile virus in Athens earlier in July and at least five other cases have been reported, Greece's disease control and prevention body said.