More than 700 attempts to carry out drug tests on Russian athletes this year have been unsuccessful, the World Anti-Doping Agency (WADA) said Wednesday, in a damning report issued just days before a key decision on the country's participation at the Olympic Games.

The WADA report said 736 tests between February 15 and May 29 were "declined or cancelled" for multiple reasons ranging from sample collection problems or athlete whereabouts.