• IAAF confirms positive ‘no-notice’ test for Rio 2016 marathon winner • Kenyan became first from her country to win gold in the event

Jemima Sumgong, the Olympic marathon champion, has tested positive for the blood booster EPO in an out-of-competition drug test in Kenya in the biggest blow yet to the credibility of the African country’s famed distance-running programme.

Sumgong, who became the first Kenyan woman to win Olympic marathon gold at last year’s Rio Games, is the London Marathon champion and was the points leader in the World Marathon Majors series. She was also in line to receive a £200,000 bonus when the current series ends in Boston on 17 April. The series said it will not now name a female winner until doping officials have resolved her case.

“The athlete tested positive for EPO following a no-notice test conducted by the IAAF in Kenya, part of an enhanced IAAF out-of-competition testing programme dedicated to elite marathon runners,” the athletics governing body said in a statement.

That programme is run jointly by the IAAF and the World Marathon Majors series. Organisers of the London Marathon announced Sumgong failed the test in February and would not be allowed to defend the title this month as she is provisionally suspended.

The Olympic champion is now the highest profile of dozens of athletes from the east African country to have failed drug tests since the 2012 Games and her case puts the country’s anti-doping failures back in the spotlight. The vast majority to fail recently were lower-level runners and Kenyan officials had claimed that their top Olympians were clean.

Sumgong is also the second Kenyan woman to test positive for EPO while leading the world marathon series. Rita Jeptoo, who won the Boston Marathon winner in 2006 and 2013, was the top runner in the world when she failed an out-of-competition test in 2014, and subsequently stripped of that year’s Boston and Chicago titles. Jeptoo, initially given a two-year ban, saw her punishment doubled to four years in 2016, after the IAAF had appealed to the court of arbitration for sport for a sterner sanction.

Tim Hadzima, the general manager of World Marathon Majors, said the body was distressed to hear reports that Sumgong had failed a drug test but “if true, they indicate that we are gaining ground in our long-standing fight against doping”.

Sumgong will now miss the London Marathon on 23 April, the race’s chief executive said. “We are determined to make marathon running a safe haven from doping,” Nick Bitel said.

Bitel said Sumgong’s test was part of the world marathon series’ efforts to target 150 top marathon runners in out-of-competition tests every year. The World Marathon Majors awards prizes to runners with the top finishes over six of the most prestigious annual marathons, plus the Olympics and world championships.

Sumgong can request that her B sample is tested, however, but if that is also positive she faces at least a two-year suspension.

The 32-year-old Sumgong’s victory in Rio capped an outstanding performance by Kenya in track and field at the Olympics, when the country finished second to the United States in the medal table. Eliud Kipchoge also won gold in the men’s marathon for a Kenyan sweep.

But Kenya’s Olympics were also undermined by a series of scandals involving coaches and officials, and its reputation has been seriously harmed by a spike in doping cases over the last five years.