Four Russian athletes have tested positive for the banned drug meldonium.
At least 16 Russian sportspeople, including tennis player Maria Sharapova, have tested positive for the substance since it was banned by the World Anti-Doping Agency on 1 January.
The latest four are yet to be named.
Russia’s athletics federation is suspended from international competition for its alleged involvement in widespread doping, with a decision on potential reinstatement due in May.
Dmitry Shlyakhtin, head of the All-Russia Athletic Federation, said the latest positive tests will not “aggravate” that “complex” decision.
Russia’s international ban – which includes this summer’s Rio Olympic Games – applies only to its athletics federation and followed a Wada report last year that alleged “state-sponsored doping”.
Last week, Russia’s four-time breaststroke world champion Yuliya Efimova failed an out-of-competition test.
World number seven Sharapova, meanwhile, failed a drugs test at the Australian Open.
The 28-year-old said she had been taking meldonium since 2006 for health reasons.
According to Wada, a substance may be “considered” for the prohibited list if it meets two of the following three criteria:
- Enhances performance
- Poses a threat to athlete health
- Violates the spirit of sport
A substance can be added to the prohibited list without first featuring on the watch list.