Follow-up tests on backup urine samples by Tour de France champion Floyd Landis found traces of synthetic testosterone, the French sports newspaper L'Equipe reported Monday.

The tests on seven "B" samples clearly showed traces of the banned substance, the paper said on its Web site. Landis had insisted the follow-up tests weren't necessary because the primary "A" samples tested negative for banned substances during the Tour.

The tests were done at France's national anti-doping laboratory of Chatenay-Malabry outside Paris. L'Equipe said the lab used a technique that can distinguish synthetic from natural forms of testosterone, a male sex hormone. The lab is the same one that revealed Landis' positive test for elevated testosterone to epitestosterone levels after he won the 17th stage of last year's Tour.

Pierre Bordry, president of the French anti-doping agency, told The Associated Press the tests were concluded this weekend but he didn't know the result because they were sent directly to the U.S. Anti-Doping Agency, which requested the tests.

Landis spokesman Michael Henson said Monday the head of the French lab prevented the cyclist's expert, Paul Scott, from entering the lab Sunday to witness the testing.

"Such behavior constitutes a clear and direct infringement of Landis' rights while casting severe doubt on the integrity of an already dubious process," Henson said in a statement.

Bordry confirmed the incident had taken place but said it stemmed from a prior agreement stipulating that Landis' expert would attend the test with two USADA experts.

Scott was excluded Sunday because USADA experts didn't show up, Bordry said.

USADA general counsel Travis Tygart said agency rules prevent him from commenting on an active case.

Landis lashed out at USADA in a statement Monday, saying the incident in which his expert was barred from the French lab was "yet another in a series of malicious actions."

"I'm infuriated by the behavior of USADA" and the French lab, Landis said. "Together, they have turned this proceeding into a full-scale attack on my civil rights and a mockery of justice."

The 31-year-old cyclist has an arbitration hearing May 14 in California, where he is expected to question the practices of the French lab. Landis wanted the follow-up tests on the backup samples conducted at the UCLA lab that handles much of USADA's testing, but the machine it uses is under repair.

If doping accusations against Landis are upheld, he faces a two-year ban from competition. He also would be the first rider in the 104-year history of the Tour to be stripped of the title. He already has agreed not to compete in this year's event while the case is pending.