LONDON -- Chris Froome's renewed protestations of innocence on Thursday were accompanied by doubts about why the four-time Tour de France champion was not immediately suspended for failing a doping test.

Froome has been ordered to explain to the International Cycling Union why a urine sample he provided at the Spanish Vuelta in September showed a concentration of the asthma drug salbutamol that was twice the permitted level.

While accepting the case is "damaging" for a sport scarred for years by doping scandals, Froome maintained Team Sky has the evidence to prove he is not guilty of cheating.

"I know that within me fundamentally I have followed the protocol and I have not overstepped any boundaries," Froome said, "and I hope by the end of this process that will be clear to everyone and I'll be exonerated of any wrongdoing."

Froome offered a defence of his integrity in an interview with Sky, the broadcaster that owns his cycling team.

"I am being tested every single day of the race that I am in the leader's jersey, I knew I was being tested," Froome said. "We also have a wealth of information from within the team of what I ate every single day, how many times I have stopped to pee every day.

"The detail of the information that we have been able to provide is vast."

Sky and the UCI confirmed Froome's failed test early Wednesday in response to media reports.

Rival rider Tony Martin said he believes something is amiss with the UCI's handling of the case.

"I am totally angry," the German cyclist wrote on Facebook. "There is definitely a double standard being applied in the Christopher Froome case. Other athletes are suspended immediately after a positive test. He and his team are given time by the UCI to explain it all. I do not know of any similar case in the recent past. That is a scandal, and he should at least not have been allowed to appear in the World Championships.

"Not only the public but also I have immediately the impression that there is wheeling and dealing going on behind the scenes, agreements are being made and ways are being sought as to how to get out of this case. Do he and his team enjoy a special status?"

The UCI did not immediately respond to a request for comment about its actions, which Martin denounced as a "major blow to the difficult anti-doping fight."

"We need a (consistent) and transparent approach by the UCI," Martin wrote. "What is going on here is (inconsistent), not transparent, unprofessional and unfair. Our credibility is at stake!"

Sky said Froome had to take an increased dosage of salbutamol without exceeding the permissible dose after experiencing "acute asthma symptoms" during the final week of the Vuelta.

Salbutamol helps expand lung capacity and can be used as a performance-enhancing drug to increase endurance. Commonly marketed as Ventolin, salbutamol is classified as a beta-2 agonist and WADA allows it to be taken through inhalation only, in limited amounts.

"It's sad seeing the misconceptions that are out there about athletes & salbutamol use," Froome wrote on Twitter. "My hope is that this doesn't prevent asthmatic athletes from using their inhalers in emergency situations for fear of being judged. It is not something to be ashamed of."