The International Cycling Union has defended its actions after it was confirmed that Lance Armstrong returned test samples with traces of corticosteroids four times during the 1999 Tour de France.

It had previously been known that the former US Postal rider, who in January confessed to drug use, had tested positive for the substance once, but the UCI has confirmed a leaked internal memo stating that there were actually four positive tests.

At the time, the UCI accepted that the traces came from cream used to treat saddle-soreness after Armstrong produced a therapeutic use exemption (TUE) certificate. He admitted this year the medical certificate had been backdated.

In a nine-page document explaining the background, the UCI also confirmed that re-tests of Armstrong's 1999 samples in 2005 also showed the presence of the blood-boosting agent EPO. The lack of B samples to test, however, made it impossible to charge Armstrong with a doping offence.

The UCI's document states in relation to the corticosteroid findings: "It should be stressed that this case was handled knowing only the facts which were apparent at that time. For example, the UCI did not know that the medical certificate handed over to Dr. Schattenberg, a member of UCI's Anti-doping Commission, in July 1999 had been post-dated. Armstrong only admitted this during his interview with Oprah Winfrey, which was broadcast on 17 January 2013."

In relation to the EPO, the UCI said the re-tests could not be taken as proof of doping.

The UCI document states: "In 1999, no test had yet been developed that could detect EPO, so the samples taken during the 1999 Tour de France were not tested for EPO.

"In 2005, samples taken from Lance Armstrong at the 1999 Tour de France were retested in a scientific research program of the anti-doping laboratory of Chatenay-Malabry, Paris.

"According to the research results EPO was found in Armstrong's samples. As indicated by the laboratory, and later also in the Vrijman report, these research results did not constitute valid proof of the presence of EPO under the anti-doping rules.

"Until his public confession in an interview with Oprah Winfrey broadcasted on 17 January 2013, Armstrong has always denied that he had ever used EPO."