Two female Kenyan athletes - 400 metres runner Joyce Zakary and 400m hurdler Francisca Koki Manunga - have been suspended following positive doping tests here at the International Association of Athletics Federations World Championships.
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."
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.
April 2015: Leading Kenyan athletes protest at "unprofessional" agent suspensions
April 2015: Athletics Kenya suspends Italian and Dutch agencies pending investigations into doping cases
March 2015: Every African country should have own anti-doping agency, claims Diack
February 2015: IAAF's Kenya laboratory ready soon as new World Marathon Majors deal to boost anti-doping efforts launched
January 2015: Jeptoo to miss Rio 2016 after receiving two-year doping ban