Mr Valls was booed as he went to sign the book of condolence at the memorial service on the Promenade des Anglais. Mohamed Lahouaiej Bouhlel killed at least 84 people and injured hundreds of others as he rammed a 19-tonne lorry into the crowd at the Bastille Day celebrations on Thursday night.
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The 31-year-old zigzagged through the crowd in a bid to cause maximum casualties and was shot dead by police after he pulled out a gun and opened fire.
Families of the dead and some of those injured gathered at the site of the massacre to remember the victims at the Moment du Centenaire in a park on the street.
Mr Valls attended the service alongside the Mayor of Nice, Philippe Pradal, the regional president Christian Estrosi and the reigning prince of nearby Monaco, Prince Albert.
The crowd cheered to celebrate the work of the emergency services. They broke in applause and raised their fists in the air when they heard the French national anthem.