The U.S. presidential candidates have condemned an attack carried out by a man who drove a truck into crowds of people celebrating France’s national day in Nice, killing at least 84 people.

Republican Donald Trump declared “this is war” and Democrat Hillary Clinton vowed “we will not be intimidated.”

Trump cancelled his Friday plans to announce a vice presidential running mate “out of respect for this horrific situation.”

Speaking on Fox News’ “The O’Reilly Factor” Trump said that if elected he would ask Congress for a “declaration of war” to combat global terrorism.

“This is war. If you look at it, this is war. Coming from all different parts,” Trump said.

“And we’re dealing with people without uniforms. In the old days, we would have uniforms. You would know who you’re fighting.”

Clinton said that “every American stands in strong solidarity with the people of France, and we say with one voice: We will not be intimidated. We will never allow terrorists to undermine the egalitarian and democratic values that underpin our very way of life.”

Speaking on the same program, Clinton stressed the U.S. need to “strengthen our alliances” with European partners and NATO.

“We’ve got to do more to understand that this is a war against these terrorist groups, the radical jihadist groups,” she said. “It’s a different kind of war.”

Clinton also called for “an intelligence surge” to improve information exchange across the Atlantic

French Prime Minister Manuel Valls said the government is declaring three days of national mourning after the attack in Nice. Speaking after an emergency meeting, Valls said the national mourning would begin Saturday.

He confirmed that a measure extending the country’s state of emergency would go before lawmakers next week.