(CNN) Doping bans on 28 Russian athletes were overturned on Thursday, throwing the International Olympic Committee's policy on Russian doping into chaos just over a week before the start of the Winter Olympics in South Korea.

The Swiss-based Court of Arbitration for Sport (CAS) upheld the appeals of athletes given lifetime Olympic bans for doping violations during the 2014 Sochi Winter Games, saying there was insufficient evidence to show they had broken the rules.

The ruling means that athletes' 2014 results are reinstated and they could now seek to participate in the Winter Games in Pyeongchang, which open on February 9.

Russian cross-country skiing star Alexander Legkov , who won gold at Sochi 2014, is among those whose bans were lifted.

In a further 11 cases, CAS ruled that doping violations had been committed but that lifetime bans were not justified and the punishments were cut to a ban for the 2018 Games alone.

The IOC said the decision "may have a serious impact on the future fight against doping," and added that it could yet appeal the decision at the Swiss Federal Tribunal, the country's highest court.

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