Kenya's Rita Jeptoo, winner of the Boston and Chicago marathons, has been banned for two years after failing a drugs test, Athletics Kenya (AK) said.
The biggest doping scandal to hit the east African country in recent years, Jeptoo's case has focused attention on Kenyan athletes who are among the world's best middle and long distance runners but have failed a number of drug tests.
Kenya's sports minister this week said the rise in doping has "embarrassed" his country. David Rudisha, the Olympic 800 metres champion, said he fears for Kenya's hard-won reputation after repeat allegations of doping.
"AK followed due process in her (Rita Jeptoo) matter and it was appropriate that she serves a two-year ban," AK Chief Executive Isaac Kamande said.
Jeptoo, provisionally suspended from athletics after the A sample proved positive, had asked for a B check which also tested positive for a banned substance.
Jeptoo,33, has denied doping, telling reporters last year that the accusations against her were "lies".
She could not be reached for comment on Friday.
Dozens of Kenyan athletes have failed dope tests in the past two years. Kenyan government officials have blamed the growing doping cases on foreign agents and AK's failure to educate its athletes properly.
Kenya on Wednesday signed a partnership agreement with Chinese and Norwegian anti-doping agencies to help root out drugs cheats.