A woman holds flowers to pay tribute to the victims of the Bastille Day truck attack in Nice in front of the French embassy in Rome, Italy, July 15, 2016.
U.S. President Barack Obama, Russian President Vladimir Putin and European and Asian leaders meeting for a summit in Mongolia joined in condemnation of what they called a terrorist attack in messages to French President Francois Hollande.

Police sources said the truck was driven by a 31-year Tunisian known to authorities for petty crime but not Islamic radicalism, who was eventually shot dead after an exchange of gunfire with police.

Dozens more people were injured. The dead included numerous foreign tourists and students, and 10 children and teenagers.

European Council President Donald Tusk, speaking in the Mongolian capital Ulaanbaatar, captured the global shock when he tweeted of the "tragic paradox that the subject of NiceAttack was the people celebrating liberty, equality and fraternity".

German Chancellor Angela Merkel said on the sidelines of the Asia Europe Meeting (ASEM) in Mongolia: "All of us who have come together at the ASEM summit are united in our feeling of disbelief at the attack of mass murder in Nice."

It was the third mass killing in Europe by suspected Islamist militants in eight months after multiple attack in Paris and Brussels linked to Islamic State.

New British Prime Minister Theresa May, whose country has just upset Paris and other European capitals by voting to leave the European Union, said Britain stood "shoulder to shoulder" with France.

Putin, whose relations with the West have been strained over Russian actions in Ukraine and Syria, went on Russian television to convey his condolences to Hollande after apparently being unable to reach him by telephone.

"Dear Francois, Russia knows what terror is and the threats that it creates for all of us. Our people have more than once encountered similar tragedies and is deeply affected by the incident, sympathizes with the French people, and feels solidarity with them," he said, adding that Russian citizens were among the victims in Nice.

In another gesture possibly aimed at healing rifts, Russian Foreign Minister Sergei Lavrov went to the French Embassy in Moscow with visiting U.S. Secretary of State John Kerry to lay flowers in memory of the victims.