Minute de silence au départ / Minute of silence at the start this morning #PrayForNice pic.twitter.com/FMihoxKNUZ

— Tour de France™ (@LeTour) July 15, 2016

Tour director Christian Prudhomme, following a meeting with police, government, regional and security officials, said: "It's a day of mourning, for France and for the Tour de France. The Tour de France will continue in sobriety and with dignity.

"We wish today to be dignified, in tribute to the victims. We are thinking about the families, we offer our condolences to everyone who has been affected, who has lost a loved one. To everyone who is injured, in flesh and in their being.

"We asked questions of ourselves, effectively. But we think, in agreement with the state authorities, that the race should continue, and we mustn't give in to pressure of people who want us to change our way of life."

There was a minute's silence held at the start of Friday's 13th stage, a 37.5-kilometres time-trial from Bourg-Saint-Andeol to La Caverne du Pont-d'Arc.

Bourg-Saint-Andeol is 300km north west of Nice, on the south coast of France.

President Francois Hollande on Friday declared three days of national mourning until July 18, with flags to be put at half-mast, and the state of emergency declared after the November terror attacks in Paris has been extended for three months. It had been due to end on July 26.

The Tour's official Twitter feed wrote "The heart of the Tour beats for Nice."

Le coeur du Tour bat pour Nice. #NousSommesUnis pic.twitter.com/2xtmfqWgWf

— Tour de France™ (@LeTour) July 15, 2016

Security was already on the agenda at the Tour after swollen crowds on Mont Ventoux led to the farcical sight of Chris Froome, wearing the race leader's yellow jersey, crashing and running up the finishing ascent.

Froome, who lives in Monaco, wrote on Twitter: "Thoughts are with those affected by the horrific terror attack in Nice."

The Tour's publicity caravan - usually a raucous, loud and party-like train of vehicles - was silent on Friday and security was reinforced.

Froome was due to be the final rider to roll down the starting ramp on Friday afternoon after being restored to the yellow jersey by the race jury.

Huge Bastille Day crowds caused a television motorbike to stop suddenly and spark the crash near the finish on Thursday, leaving Team Sky leader Froome without a working bike and with support vehicles unable to get through to him immediately, so he set off on foot.

It appeared the chaos would cost Froome the yellow jersey, but race officials amended the results to ensure the British rider and former team-mate Richie Porte, also caught in the crash, did not lose out.

By the time the official stage 12 results were published, Froome had extended his lead over fellow Briton Adam Yates to 47 seconds.

Friday's time-trial should suit Froome and he was expected to enhance his advantage.