Sabotage struck the Tour de France on Sunday as leader Bradley Wiggins was forced to call a truce on stage 14 as a result of around 30 punctures caused by tacks on the road.
The riders were hit by the tacks - the race director confirmed their presence afterwards - towards the end of an absorbing stage.
At the summit of the Mur de Peguere, the second of two category one climbs on the day's 191-kilometre route from Limoux to Foix, Wiggins and defending champion Cadel Evans (BMC Racing) were among those to suffer flat tyres.
As Luis-Leon Sanchez (Rabobank) broke free of the day's escape to solo to victory, Wiggins called for the peloton to neutralise their effort to allow Evans to return to the group as they finished more than 18 minutes behind.
It left the top of the general classification unchanged and with Wiggins facing six more days' racing to keep the maillot jaune on a permanent basis as the Tour's first British winner.
Jean-Francois Pescheux, competitions director of Tour organisers Amaury Sports Organisation, said: "We don't know who it was. No-one saw anything.
"We've found some of the tacks. They're the kind of tacks you use in mattresses or carpets. They were obviously thrown by a spectator.
"There were around 50 riders together in the front peloton at the top and about 30 of them ended up with punctures. Some of them had three or four nails in their tires.
"We couldn't neutralise it straight away because we didn't know what had happened. Fortunately Sky neutralised the race."