KIEV, Ukraine — Two Ukrainian sprinters have been charged with doping offenses and stopped from competing at the world athletics championships, which start Friday.

Olesya Povkh and Olha Zemlyak, both former medalists at major championships, were named by the Ukrainian Athletics Federation said in a statement Thursday.

The federation said that Povkh and Zemlyak had written to the International Association of Athletics Federations but “their explanations … were found to be insufficient to explain the abnormal test results.”

The IAAF’s Athletics Integrity Unit said each faced a charge of “the use of a prohibited substance” and had been suspended pending the outcome of the case.

Zemlyak’s coach Serhiy Basenko was also removed from Ukraine’s world championship delegation, the federation said.

Povkh won an Olympic bronze medal in the women’s 4×100-meter relay in 2012, and had been due to race the 100 and 4×100 at the world championships in London.

Zemlyak took silver in the 400 at the European championships in 2014. She was due to compete in the 400 and 4×400 in London.

Ukrainian track and field has been hit hard by doping investigations in recent years, with javelin thrower Oleksandr Pyatnytsya and Denys Yurchenko both stripped of Olympic medals.

The world championships will start without an official Russian team as the country remains suspended from international track and field due to widespread drug use. However, 19 Russians will compete as so-called “neutral athletes” after the IAAF examined their history of anti-doping tests.