A concealed motor was found on a bike being used by Belgian cyclist Femke Van den Driessche at the world cyclo-cross championships, the head of the International Cycling Union (UCI) said on Sunday, confirming the first such case at a top-level competition.
"It's absolutely clear that there was technological fraud. There was a concealed motor. I don't think there are any secrets about that," UCI president Brian Cookson told a news conference.
The bike was seized on Saturday after Van den Driessche, one of the race favourites, was forced to withdraw from the women's under-23 race because of a mechanical problem.
Van den Driessche, 19, denied that she had on purpose used a bike with a concealed motor, saying that it was identical to her own but belonged to a friend and that a team mechanic had given it to her by mistake before the race.
"It wasn't my bike, it was that of a friend and was identical to mine," a tearful Van den Driessche told Belgian TV channel Sporza.
"This friend went around the course Saturday before dropping off the bike in the truck. A mechanic, thinking it was my bike, cleaned it and prepared it for my race," she added, insisting that she was "totally unaware" it was fitted with a hidden motor.
"I feel really terrible. I'm aware I have a big problem. (But) I have no fears of an inquiry into this. I have done nothing wrong," she said.
If found guilty of cheating the rider faces disqualification, a six-month suspension and a fine of up to 200,000 Swiss francs (180,000 euros, $195,000).
"We've heard some stories for a long time now about the possibility of this. We have been alive to a potential way that people might cheat and we have been testing a number of bikes and a number of events for several months," Cookson said.
"I am committed and the UCI is committed to protecting the riders who do not want to cheat in whatever form and to make sure that the right riders win the race.
"We have been looking at different methods of testing this kind of technology and we tested a number of bikes yesterday and one was found.
"We will keep testing both at this event and subsequent events. Whether this means that there is widespread use of this form of cheating remains to be seen.
Cookson said that the matter would next go before the UCI's disciplinary commission.
Etixx team manager Patrick Lefevere called for a "lifetime suspension for the cheat", while Belgian national team coach Rudy De Bie was outraged by the discovery.
"I never thought that such schemes were possible. It's a scandal that Femke's entourage have deceived the Belgian federation," he said.
The news is a fresh blow to a sport still recovering from the Lance Armstrong doping scandal after the disgraced American cyclist admitted to cheating throughout his career in 2013 following years of denials and ruthless attacks on his accusers.
However, it isn't the first time eyebrows have been raised over suspicions of "mechanical doping" - the term used for bikes found to have a hidden motor inside the wheels or frame that serves as an illegal aid to the rider.
Last year's Tour de France champion Chris Froome faced accusations of using a motorised bicycle, while Fabian Cancellara's 2010 victory in the Tour of Flanders also stirred a debate.
He denied the accusations before, a week later, racing off into the distance to win Paris-Roubaix even more impressively.
Cyclo-cross races are held on technical and hilly 2.5 to 3.5-kilometre circuits and approximately last one hour.
Riders complete several laps of the course and can sometimes be forced to dismount to climb steep slopes and bypass obstacles. The event is most popular in traditional road cycling countries such as Belgium, France and the Netherlands.