With the sports world's attention focused on Maria Sharapova's positive test for meldonium, three other doping cases among elite Russian athletes have emerged in the last two days.

World champion speedskater Pavel Kulizhnikov, Olympic gold medal-winning ice dancer Ekaterina Bobrova and national team volleyball player Alexander Markov are all suspected of taking meldonium, according to Russian reports.

The 21-year-old Kulizhnikov has won five world championship gold medals since the start of 2015. He is also world record-holder in the 500 meters.

Russian speedskating coach Dmitry Dorofeev did not say when or where Kulizhnikov tested positive for meldonium, which has been on the World Anti-Doping Agency's list of banned substances since Jan. 1. Once used in the Soviet military, meldonium is sold in Eastern Europe as a treatment for heart and circulation problems.

Dorofeev told Russia's Tass news agency that Kulizhnikov had used meldonium while it was legal.

"We all know that meldonium was banned. He hasn't been taking it for a year," Dorofeev said. "We are clean, we didn't take the substance. How it got in there, we don't know."

Kulizhnikov previously served a doping ban between 2012 and 2014 after a positive test for methylhexamine.

Separately, the governing body of ice skating confirmed Tuesday that Bobrova was provisionally suspended. The former Olympic gold medalist and European champion has told Russian media she tested positive for meldonium at January's European championship, where she finished third.

In a third case, Russian volleyball federation general secretary Alexander Yaremenko told Tass that Markin had tested positive for meldonium.

"We've declined to test the 'B' sample. The signs it (meldonium) was consumed are clear," Yaremenko said. "The Dynamo club took a course of this substance in December and the doping test was taken Jan. 9 at a training camp."

Since it was banned at the start of the year, two Ukrainian biathletes and Russian cyclist Eduard Vorganov have also tested positive for meldonium.