(Reuters) - Italy's 2008 Olympic 50km race walk champion Alex Schwazer has lost his appeal against a provisional ban for a doping violation and was suspended for eight years, the Court of Arbitration for Sport (CAS) said on Thursday.

Schwazer, who returned from a previous doping ban to lead Italy to the 50km world race walking team title in Rome this year, tested positive in May for a steroid that he said he had not knowingly taken.

The International Association of Athletics Federations (IAAF) imposed a provisional ban on the 31-year-old but the walker took his case to CAS with his lawyer claiming the athlete's sample had been tampered with.

Schwazer previously served a three-and-a-half-year suspension after admitting to using the blood booster erythropoietin (EPO) in 2012.

Schwazer asked CAS to treat his appeal as an urgent request ahead of the Rio Olympics but this was dismissed and sport's highest court instead initiated an expedited arbitration procedure to rule on the case.

"All competitive results obtained by Alex Schwazer from and including 1 January 2016 are disqualified with all resulting consequences, including forfeiture of medals, points and prizes," CAS said in a statement.

(Reporting by Sudipto Ganguly in Mumbai; Editing by John O'Brien)