PARIS - An unacceptable breach of medical confidentiality was how International Olympic Committee chief Thomas Bach described the recent string of leaks by the Russian cyber-espionage group Tsar Team, also known as Fancy Bears.

The hacking group released information on sports stars including US Olympic gymnast Simone Biles, a four-time gold medallist in the Rio Games, and tennis champions Venus and Serena Williams. In their most recent release on Thursday, the group published confidential data of 25 athletes including British Tour de France-winning cyclists Bradley Wiggins and Chris Froome.

Bach, the German IOC leader, defended the athletes concerned and said his organisation gave the World Anti Doping Agency (WADA) their full support. "This is an unacceptable and outrageous breach of medical confidentiality that attempts to smear innocent athletes who have not committed any doping offence," Bach said.

"The IOC fully support the actions taken by WADA to deal with the leak, including the measures that are being taken to bring this activity to an end with the help of IT experts and in requesting assistance from the Russian authorities," Bach said in an IOC statement.

"I have informed the WADA President, Sir Craig Reedie, that the IOC will also assist WADA in any way required, including communicating with the Russian authorities." The Kremlin has already said it was ready to help, while also denying any Russian involvement in the hacking.