The four-time world champion, her country's best-known swimmer, tested positive for meldonium soon after it was added to the World Anti-Doping Agency (WADA) banned list at the beginning of this year.

A controversial athlete, the 24-year-old also served a 16-month ban for doping having failed for banned steroid DHEA in 2013.

Efimova claimed to have not been told that meldonium - a heart attack drug which is thought to boost endurance - had been added to the banned list on January 1.

WADA's subsequent admission that more research is required on the drug has given her hope, however.

If below one microgram of meldonium was detected and the failed test came before March 1, they ruled a negligence or no fault verdict could be reached.

FINA decided last month not to lift the case against Efimova until a hearing of the FINA Anti-Doping Panel scheduled for May 30, meaning she was barred from training in America and competing in the ongoing European Championships here.

Her case will now go directly to the Court of Arbitration for Sport (CAS), according to Russian Swimming Federation President and FINA Bureau member Vladimir Salnikov, with the ban lifted in the meantime.

It is not yet clear when the CAS hearing will take place.

"I can confirm the information that the temporary suspension has been lifted," Russian swimming head coach Sergey Kolmogorov added.

"She is now allowed to practice anywhere in the world, including at the base in Los Angeles."

Efimova won the 100 metres breaststroke title at last year's World Championships in Kazan, as well as the 50m world title in 2009 and the 50m and 200m double in 2013.

She faces a life ban from the sport, however, if found guilty of doping once again.

Efimova is now hoping to train under Dave Salo’s University of California/Trojan programme, Swim Vortex have reported, citing her agent, Andrey Mitkov.

This is with the aim of competing at Rio 2016.

If confirmed, this will raise eyebrows throughout the swimming world at a time when attitudes towards doping policies in the sport are already sceptical.

“I am not in favour [of the suspension being lifted] - it’s a bad signal," senior Sweden coach and former Russia head coach Andrei Vorontsov told Swim Vortex.

"I talked to swimmers and coaches before it happened and they told me they would be very angry and now it has happened and they are angry.

"It should be a lesson for those who want to find a short cut - I think she should be still out until it’s decided.”

It comes as a hearing into Maria Sharapova, another US-based Russian who has failed for meldonium, begins in London.

A verdict on the tennis player is not expected until next month.