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The former director general of Russia's anti-doping agency has admitted the country has "a serious problem", and says 40% of its drug-test violations have come in youth sports.

Russia was suspended from international athletics over doping, and must reform in order to return for the Olympics.

On Thursday, four Russian weightlifters were suspended after failing drugs tests at the World Championships.

"In Russia, the doping issue is acute, we can't deny it," said Ramil Khabriev.

Khabriev, who left his post at Rusada earlier this month, was speaking to Russian broadcaster R-Sport.

He added: "We have the most violations in anti-doping rules in comparison with other countries.

"This, of course, shows there's a serious problem. Around 40% of these violations are from youth sports, which is alarming."

The International Association of Athletics Federations (IAAF) voted to suspend Russia's athletics federation in November.

That followed the publication of an independent World Anti-Doping Agency (Wada) report that alleged "state-sponsored doping".

An IAAF taskforce is set to visit Russia in early January to check on progress towards complying with anti-doping regulations.

Since November's World Championships, the International Weightlifting Federation has provisionally banned 17 athletes, four of whom were Russian - including men's 105kg world champion Aleksey Lovchev.