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.

Tour de France 2018: stage-by-stage guide Show all 42 1 /42 Tour de France 2018: stage-by-stage guide Tour de France 2018: stage-by-stage guide Stage 1 Saturday 7 July: Noirmoutier-En-L’Ïle to Fontenay-Le-Comte (201km) Tour de France 2018: stage-by-stage guide Stage 1 profile A flat opening stage following the coastline which will expose the peloton to crosswinds from the Atlantic Ocean and is likely to end in a bunch sprint. Tour de France 2018: stage-by-stage guide Stage 2 Sunday 8 July: Mouilleron-Saint Germain to La Roche-Sur-Yon (182.5km) Tour de France 2018: stage-by-stage guide Stage 2 profile A route through the Vendee countryside with another opportunity for the sprinters to clinch a stage victory. Tour de France 2018: stage-by-stage guide Stage 3 Monday 9 July: Cholet (team time trial, 35.5km) Tour de France 2018: stage-by-stage guide Stage 3 profile A team trial around Cholet which will give an early indication as to the quality and depth of the leading groups. Tour de France 2018: stage-by-stage guide Stage 4 Tuesday 10 July: La Baule to Sarzeau (195 km) Tour de France 2018: stage-by-stage guide Stage 4 profile The visit to Brittany could be the moment for the dominant sprinter of the Tour to make his mark. Tour de France 2018: stage-by-stage guide Stage 5 Wednesday 11 July: Lorient to Quimper (204.5 km) Tour de France 2018: stage-by-stage guide Stage 5 profile A tricky stage to Finistere full of narrow roads and short, sharp climbs. Tour de France 2018: stage-by-stage guide Stage 6 Thursday 12 July: Brest – Mûr de Bretagne Guerlédan (181 km) Tour de France 2018: stage-by-stage guide Stage 6 profile The Mur de Bretagne will be scaled twice in the final kilometres in the toughest test of the first week. Tour de France 2018: stage-by-stage guide Stage 7 Friday 13 July: Fougères to Chartres (231 km) Tour de France 2018: stage-by-stage guide Stage 7 profile This is a long stage which invites a breakaway but is likely to won by a sprinter. Tour de France 2018: stage-by-stage guide Stage 8 Saturday 14 July: Dreux to Amiens Métropole (181 km) Tour de France 2018: stage-by-stage guide Stage 8 profile The sprinters could be scuppered by the Normandy crosswinds – conditions will be crucial. Tour de France 2018: stage-by-stage guide Stage 9 Sunday 15 July: Arras Citadelle to Roubaix (156.5 km) Tour de France 2018: stage-by-stage guide Stage 9 profile A testing route consisting of 22km of cobblestone split into 15 treacherous section which could claim a few casualties. Tour de France 2018: stage-by-stage guide Stage 10 Tuesday 17 July: Annecy to Le Grand-Bornand (158.5 km) Tour de France 2018: stage-by-stage guide Stage 10 profile A rare trip off the asphalt and on to a gravel road is likely to puncture a few tyres. Tour de France 2018: stage-by-stage guide Stage 11 Wednesday 18 July: Albertville to La Rosière (108.5 km) Tour de France 2018: stage-by-stage guide Stage 11 A first serious taste of the mountains, albeit on a very short stage. Tour de France 2018: stage-by-stage guide Stage 12 Thursday 19 July: Bourg-Saint-Maurice Les Arc to Alpe d’Huez (175.5 km) Tour de France 2018: stage-by-stage guide Stage 12 profile A summit finish on top of the Tour de France’s most iconic climb: Alpe d’Huez. Tour de France 2018: stage-by-stage guide Stage 13 Friday 20 July: Bourg d’Oisans to Valence (169.5 km) Tour de France 2018: stage-by-stage guide Stage 13 profile A gentler day after three stages in the mountains and one for the sprinters to contest. Tour de France 2018: stage-by-stage guide Stage 14 Saturday 21 July: Saint-Paul-Trois-Châteaux to Mende (188 km) Tour de France 2018: stage-by-stage guide Stage 14 profile A stage with four categorised climbs including a sharp climb to Mende which will hurt tired legs. Tour de France 2018: stage-by-stage guide Stage 15 Sunday 22 July: Millau to Carcassonne (181.5 km) Tour de France 2018: stage-by-stage guide Stage 15 profile Another undulating day ripe for a breakaway. Tour de France 2018: stage-by-stage guide Stage 16 Tuesday 24 July: Carcassonne to Bagnères-de-Luchon (218 km) Tour de France 2018: stage-by-stage guide Stage 16 profile A long and draining stage with three ascents in the second half to bring out the best in the elite climbers. Tour de France 2018: stage-by-stage guide Stage 17 Wednesday 25 July: Bagnères-de-Luchon to Saint-Lary-Soulan (65 km) Tour de France 2018: stage-by-stage guide Stage 17 profile The shortest regular stage for 30 years and yet a brutal one, finishing on the steep Col du Portet, which could prove decisive. Tour de France 2018: stage-by-stage guide Stage 18 Thursday 26 July: Trie-sur-Baïse to Pau (171 km) Tour de France 2018: stage-by-stage guide Stage 18 profile Some respite for the climbers after three draining days, and another chance for the sprinters to shine. Tour de France 2018: stage-by-stage guide Stage 19 Friday 27 July: Lourdes to Laruns (200.5 km) Tour de France 2018: stage-by-stage guide Stage 19 profile The famous Aspin-Tourmalet combination in the middle of this stage makes it perfect for a yellow jersey assault. Tour de France 2018: stage-by-stage guide Stage 20 Saturday 28 July: Saint-Pée-sur-Nivelle to Espelette (individual time trial, 31 km) Tour de France 2018: stage-by-stage guide Stage 20 profile A time trial with enough short climbs – including the final Col du Pinodieta – to upset the traditional time triallists. Tour de France 2018: stage-by-stage guide Stage 21 Sunday 29 July: Houilles to Paris (116 km) Tour de France 2018: stage-by-stage guide Stage 21 profile The procession into the Champs-Elysees for those that have made it, and one final opportunity for the power riders.

"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.

Froome was attacked on Thursday's stage (ITV Sport)

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.