The drug at the center of the Maria Sharapova doping case has produced 99 positive tests so far this year, the World Anti-Doping Agency said Friday.

WADA spokesman Ben Nichols told The Associated Press in an e-mail that since meldonium was banned on Jan. 1 "there have been 99 adverse analytical findings" for the drug.

Nichols did not provide details of who has tested positive.

Meldonium, a blood-flow boosting drug produced in Latvia, is most common in Eastern European and former Soviet countries, where it is often available over the counter.

Seven of the 16 confirmed cases come from Russian athletes, including Sharapova, who admitted she had tested positive on Monday at a news conference. Sharapova said she has been taking meldonium for 10 years for various health issues and did not know it had been banned.

Other cases involve athletes from Ukraine, Georgia and Sweden.

On Friday, Beckie Scott, a former Canadian cross-country skier and current chair of WADA's Athlete Committee, released a statement on behalf of the entire committee to Sir Craig Reedie, WADA's president.

She called for WADA to extend the Independent Commission report, a request that was put forth by the Athletes' Committee in November. 

"We are of the firm opinion that there needs to be further investigation into other sports in Russia, and other countries identified in the [Independent Commission] report," read the statement. "The principles of fair sport are very close to our hearts. We believe that extending the mandate will be a sign of our commitment to clean sport, and a sign that the voice of the clean athlete is being heard."

Athletes who fail doping tests can face a ban of up to four years for a first offense, but substantial reductions can be imposed if they demonstrate that they did not intend to enhance their performance.

Sharapova is one of four Olympic medalists to have tested positive for meldonium. The others are Russian speed skater Semyon Elistratov, Russian ice dancer Ekaterina Bobrova and Georgian wrestler Davit Modzmanashvili.

WADA announced in September that meldonium, which was once used to help boost the endurance of Soviet troops, would be banned from 2016, citing evidence of the drug's performance-enhancing benefits and widespread use in international sports.

Since Sharapova announced that she tested positive, the Russian government has criticized WADA. Foreign Minister Sergei Lavrov said Thursday that meldonium should never have been banned, arguing that it doesn't enhance performance.

Within Russia, senior figures have been shifting blame between federation officials, team doctors and the athletes themselves. The head of the speedskating federation has said he suspects some people of spiking their teammates with meldonium so that they would test positive.

On Friday, Sports Minister Vitaly Mutko told the Interfax news agency that an investigation was under way into how so many athletes tested positive.

"I share collective responsibility," he said, adding that the answer was not to reduce Russia's reliance on sports medications but to develop new drugs that are not banned.

"When we aren't creating our own, we get caught using Latvian or Chinese substances," Mutko said. "We should have our own scientific research activity in high-level sport."

With files from CBC Sports