Team Sky have blamed the punctures suffered by Richie Porte and Geraint Thomas during yesterday's stage five of the Tour de France on tacks deliberately thrown onto the road by spectators.

Porte and Thomas were two of a handful of riders to suffer flat tyres during the 228.5-kilometres run from Cagnes-sur-Mer - a stage won by Mark Cavendish on the seafront in Marseille.

Neither Porte nor Thomas lost time, although the stop for a change of tyre and another standing start caused further pain for Thomas, who has been riding on a cracked pelvis since a crash on the opening stage.

"Richie (Porte) and G (Thomas) both experienced flat tyres, and we think they might have been down to people placing tacks on the road," Team Sky sports director Nicolas Portal said on the team's website.

"They were in the tyres when we inspected them after the race, and a few other teams also experienced similar problems.

"That's a bit of a worry, but thankfully nobody was hurt."

Chris Froome avoided both the tacks and two major crashes near the finish to remain in seventh place overall - just three seconds off the leader, former Team Sky man Simon Gerrans who is now riding for Orica GreenEdge.

Last year, Sir Bradley Wiggins earned the title 'Le Gentleman' after stage 14 of the Tour to Foix came under attack from saboteurs, with Wiggins - in the yellow jersey - slowing the peloton to allow rivals to catch up after they stopped to deal with punctures.