The US President said his country stood by France, "our oldest ally" after "what appears to be a horrific terrorist attack".
He added that the he has been in touch with French officials and "offered any assistance that they may need to investigate this attack". My thoughts and prayers are with the families and loved ones of those lost and wounded.
"We stand in solidarity and partnership with France, our oldest ally, as they respond to and recover from this attack", stated the U.S. president. "It is hurting but it is strong, and she will be strong, always stronger than the fanatics who wish to hurt us", said French president Francois Hollande.
In a tweet he professed solidarity with the people of Nice and the Alpes-Maritimes department.
Major events in France have been guarded by troops and armed police since the Islamic State attacks previous year, but it appeared to have taken many minutes to halt the progress of the truck as it tore along pavements and a pedestrian zone.
"I am shocked to hear about the terrorist attack on an innocent crowd of people gathered to celebrate the Bastille Day in Nice, France".
"This cowardly attack only strengthens our commitment to our alliance and to defeating terrorism around the world".
"Israel condemns in the strongest terms last night's horrific attack in Nice".
"I had to protect my face from flying debris".
Vocative has reported that some ISIS supporters have been celebrating the Nice attack.
France's ambassador to the United States, Gerard Araud, characterized the events in Nice as a "terrorist attack".
"An Garda Síochána will, of course, be liaising closely with their French and other global counterparts about the attack and continue to take whatever measures are necessary to deal with the threat from terrorism".
"France is filled with sadness by this new tragedy", Hollande said, noting several children were among the dead in what he said he had no doubt was an act of terrorism.
Scotland's First Minister Nicola Sturgeon wrote on Twitter: "Dreadful reports from Nice. Thoughts with all involved".
"We do know that it fits a pattern of violence perpetrated against civilians and promised by radical Islamic terrorists, which already has savaged Paris, Brussels, Istanbul, and even locations in our own country".
It was not immediately clear who would have been behind an attack, but France has recently seen a spate of dramatic assaults from by jihadist groups, including the Islamic State group which straddles Iraq and Syria.
"Heart-to-heart, we share the pain of the French people", the Foreign Ministry of Turkey said. "We will provide whatever support is needed".
Since the beginning of past year, terrorists have targeted France in a series of shootings and bombings mostly aimed at social scenes, including a November massacre that killed at least 130 people. Meanwhile, a Downing Street spokesman says the Prime Minister is being kept up to date on events in Nice, adding: "Our thoughts are with all those affected by this bad incident on what was a day of national celebration".
"We have third generation immigrants that came there from Morocco, Algeria, Libya, Tunisia. and even when their children are born in France and their children's children are born in France, they don't consider themselves French", he said.
"For a big truck like that to get actually onto the promenade and then to go in a fairly straight line along there, looked to me like a very deliberate act", the reporter said.