Truck plows into crowd in Nice, France, many injured - paper

Members of the Australian French community cry as they sing the French national anthem during a vigil in central Sydney, Australia, July 15, 2016 to remember the victims of the Bastille Day truck attack in Nice. REUTERS/David Gray

NICE, France (Reuters) - French authorities were trying to determine on Friday whether a Tunisian who killed at least 84 people by ploughing a truck into Bastille Day crowds had acted alone or with accomplices, but said the attack bore the hallmarks of Islamist militants.

Thursday night's attack in the Riviera city of Nice plunged France into new grief and fear just eight months after gunmen killed 130 people in Paris. Those attacks, and one in Brussels four months ago, shocked Western Europe, already anxious over security challenges from mass immigration, open borders and pockets of Islamist radicalism.