MOSCOW (AP) — Russian 400-meter runner Nadezhda Kotlyarova says she has tested positive for the banned substance meldonium.

The case adds to Russian track and field's difficulties as the country tries to persuade international authorities to lift a blanket ban on Russian athletes implemented in November in the wake of a major doping scandal.

Kotlyarova tells Russia's Tass agency that she failed a drug test at last month's Russian indoor championships in Moscow and is protesting her innocence.

She says the spate of positive tests for the endurance-boosting meldonium, which was added to the banned list from Jan. 1, is "injustice," adding that she intends "to see this situation out to the end."

Russians make up more than half of the more than 20 meldonium doping cases identified so far, with Maria Sharapova the best-known athlete to have been suspended. On Friday, the World Anti-Doping Agency said there had been 102 failed tests for meldonium this year, though only a small fraction of athletes' names have so far been made public.

The 26-year-old Kotlyarova raced at last year's world championships in Beijing, reaching the semifinals, and was also part of the Russian relay team which won silver in the 4x400m at the 2013 European indoor championships.

She played no part in this week's world indoor championships in Portland because Russia was suspended from global track and field by world governing body the IAAF in November after a WADA report detailed systematic, state-sponsored drug use.

At its last council meeting earlier this month, the IAAF left Russia's ban in force, saying "significant work" remained to be done before Russia meets international standards. Russia now runs the risk of being barred from the track and field competitions at August's Olympics in Rio de Janeiro, an unprecedented humiliation for such a major sporting power.

The IAAF did not respond to a request for comment on Kotlyarova's case. If confirmed to involve meldonium, it would be the third such case in track and field worldwide after former world 1,500m champion Abeba Aregawi of Sweden and the former European indoor 800m champion Nataliya Lupu of Ukraine.