Kiprop, 28 -- world champion in 2011, 2013 and 2015 -- is believed to have failed an out-of-competition test.

While the Kenyan authorities have not yet confirmed that it was Kiprop, local media have been reporting that another leading runner has failed a test.

The news will come as a huge blow to both Athletics Kenya and the Anti-Doping Agency of Kenya, as both organisations have been heavily criticised in recent years for being soft on drugs.

More than 40 Kenyan athletes have failed tests in recent years, including three-time Boston Marathon champion Rita Jeptoo and Olympic marathon champion Jemima Sumgong.

Kiprop gained the Olympic gold in 2008 when Bahrain's Rashid Ramzi was stripped of his victory for failing a drug test.