Zakary, 29, took nearly half a second off her national 400m record in the opening round, reducing it from 51.14sec to 50.41 and qualifying equal third fastest.

Koki Manunga finished her opening round in 58.96, the second slowest time in the heats.

An IAAF statement said: “The IAAF has this evening announced that two Kenyan athletes, Koki Manunga and Joyce Zakary, have accepted provisional suspensions following positive samples provided in Beijing on the 20th and 21st of August respectively.

“The IAAF Rules dictate that the IAAF is only able to make a public disclosure once this provisional suspension is in place.

“These targeted tests were conducted by the IAAF at the athlete hotels during the pre-competition phase. The IAAF will not discuss the details of the cases as they progress through the results management process.”

Kenya’s sportsarena site said Athletics Kenya's chief executive Isaac Mwangi would not confirm or deny the tests.

"Any matter touching on doping is a matter of confidentiality until proven and the right procedure is followed,” he said.

"I will meet with the team management and the IAAF and see if I have any more information besides this." 

Mwangi added that the Kenyan runners, like most of other runners in Beijing, have undergone vigorous testing since they arrived last week.

"The doping here has been vigorous and all our athletes have been tested, I think some even up to four times so far," he said.

The news comes on the day after Nairobi policeman Nicholas Bett provided Kenya with their first gold of these Games in the 400m hurdles, setting a national record of 47.79 from the outside lane.

Javelin thrower Julius Yego won another gold medal  tonight with a massive effort of 92.72 metres, the furthest throw in 14 years.

The two failed tests will focus more unwelcome attention on the Kenyan anti-doping operation, which has been the subject of many of the allegations made in the recent documentaries made by German TV company ARD which is operating in conjunction with The Sunday Times.

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