Tour de France officials have asked French police to investigate after tacks punctured the tyres of several riders on stage 14 of the race.
Speaking on French TV, race director Jean-Francois Pecheux said any search for who was responsible for scattering the tacks on the course would be "difficult" as thousands of people lined the roadside during the stage's Mur de Peguere climb.
"It was obviously done on purpose. We have the tacks but we don't know who spread them," Pescheux added.
The stage's eventual winner Luis Leon Sanchez and other breakaway riders were minutes ahead of the peloton and were spared the apparent sabotage on the route between Limoux and Foix.
At the summit of the Mur de Peguere - the second of two category one climbs on the day's route - Tour leader Bradley Wiggins and defending champion Cadel Evans were among those to suffer flat tyres.
Evans was stood by the road for several minutes as his BMC team car was already speeding down the descent and teammate Tejay Van Garderen passed without noticing him.
At the end of the stage, Wiggins said: "What can you do? It's something we can't control. There's nothing stopping more of that sort of stuff happening.
"It's sad. Those are the type of things we have to put up with as cyclists.
"I think people take that for granted sometimes, just how close they can get to us.
"If that happened in a football stadium, or wherever, you'd be arrested, CCTV."
Although Sanchez had broken free, Wiggins called for the peloton to slow down their effort to allow Evans to return to the group and they finished more than 18 minutes behind.
Wiggins' move left the top of the general classification unchanged with six days' racing left.
Earlier on Sunday, Wiggins told Sky News he was taking it one day at a time in his fight to become the first British Tour winner.
He said: "Every day we treat it as a one day race, that's what we have been doing since the start in Liege and every day that goes past it's a step closer to Paris and today is no exception.
"We still have to go out there and do a job and marshal the race as best as possible, think about all the little things, like fuelling well during the day because you are out there for six hours.
"It has been obvious all year that we have stated that our goal was to win the Tour De France, and that was the same in Liege and that hasn't changed. We are almost there. We are in touching distance of Paris."