The World Anti-Doping Agency (WADA) has claimed there were "serious failings" relating to drug testing methods at the Rio 2016 Olympics.

WADA conducted an Independent Observers report detailing the overall organisation of the anti-doping procedures at the Games in Brazil and was critical.

Among its findings, it was reported 50 per cent of tests on some days were cancelled due to athletes not turning up, while the management team in charge of the anti-doping staff also came under fire.

"The logistical arrangements made by Rio 2016 to support the sample collection process at official venues during the Games suffered from a number of serious failings, for various reasons, some of which were within Rio 2016's control and some were not," the report stated.

"Ultimately, many athletes targeted for testing in the Athletes Village simply could not be found and the mission had to be aborted.

"On some days, up to 50 per cent of planned target tests were aborted in this way. Some of the athletes in question were then put on mission orders for Out-of-Competition testing the following day, or targeted for In-Competition testing on subsequent days, but due to the logistical issues outlined above it was often the case that those tests could not be conducted either.

"There was a lack of coordination/unified approach among the management team in the Rio 2016 anti-doping department during the Games itself."