Two Kenyan runners have tested positive for doping at the world championships and have been provisionally suspended.

Joyce Zakary, a 400-meter runner, and hurdler Koki Manunga tested positive for unspecified substances in targeted tests after competing in Beijing, the IAAF said Wednesday.

Zakary was second in her opening heat on Monday, running a national record of 50.71 seconds in the 400m. But the 29-year-old Kenyan did not run in the semi-finals a day later despite having the eighth best qualifying time.

Manunga ran in the opening heats of the 400 hurdles on Sunday and finished sixth of seven, failing to reach the semi-finals.

“Athletics Kenya has already met with the IAAF and the athletes involved, and has begun investigating the situation which led to these results and appropriate follow-up action will be taken in Kenya,” the country’s national governing body said in a statement. “In the meantime, Athletics Kenya will provide full support and cooperation to the IAAF during (the) results management process, and will not be providing further comment at this stage.”

The Kenyans have 13 athletes currently serving doping suspensions.

The sport has been hit by doping allegations in recent weeks, with German broadcaster ARD and The Sunday Times newspaper in Britain reporting that they had obtained access to 12,000 suspicious blood tests involving 5,000 athletes.

The report says Kenya had 18 medals won by athletes under suspicion over more than a decade.

At this year’s world championships, Kenya was leading the medal standings after four days with four golds and nine overall. Some of those medals were won by veterans, including Ezekiel Kemboi and David Rudisha, who have been tested regularly for years.