Tour de France director Christian Prudhomme has called for calm from fans after Chris Froome was slapped and apparently spat at on the climb to Alpe d'Huez on Thursday.

Team Sky's Froome was struck by at least one spectator a little under seven kilometres from the summit of the famous climb and seemed to be spat at shortly after, on his way to a fourth-placed finish as team-mate Geraint Thomas took victory.

There had been fears about security on the mountain - where large crowds are within touching distance of riders - with Froome still facing lingering ill-feeling among some cycling fans following the salbutamol case in which he was cleared of wrongdoing just days before the Tour began.

Speaking on Friday, Prudhomme described the behaviour of some fans as "immoral" as he called for respect.

"We need to restore calm and respect all the riders," Prudhomme said.

"It was a very annoying climb of the Alpe d'Huez. The riders on the Tour, and champions of the Tour, must obviously be respected, as they are by the large majority of the public.

"By the roadside it was very calm for 10 days, with only a few anti-Froome or anti-Sky placards. But at a stroke, it all went up again.

"I can only renew my appeals for calm, for common sense, with regards to the riders who make up the Tour de France."

Although Froome was able to stay on his bike and keep with the leading group all the way to the summit, 2014 Tour winner Vincenzo Nibali crashed in the final few kilometres, apparently hitting a spectator, and is out of the Tour due to a fractured vertebra.

"It's a paradox that Vincenzo Nibali, who has nothing to do with Team Sky, ended up on the tarmac," Prudhomme added.

Police presence had been stepped up on the mountain, barriers were installed further down the climb than usual, and one of the most crowded points, Dutch Corner, saw fans held back by ropes.

However, four-time Tour winner Froome said he felt more could be done.

"I think the organisers had tried to put in a few special precautions to stop those kind of things happening," Froome said.

"When you've got fans touching and interfering with the riders, who are doing everything to try and get up the climb, that's not a situation anyone wants to see. That's not acceptable.

"I was pushed a few times but thankfully I stayed on my bike and didn't get knocked off.

"(Appealing for calm) is a step in the right direction but I think there are more measures that can be taken, for sure."