PARIS (AFP) - French police arrested two men in connection with the Bastille Day massacre in Nice which left 84 people dead, a source close to the investigation said on Tuesday (July 26).

"They were placed in custody while investigators seek to determine if the Tunisian (attacker) Mohamed Lahouaiej Bouhlel had logistical support," said the source.

Prosecutors believe Bouhlel had long plotted the attack in which he ploughed a 19-tonne truck into a crowd which had been enjoying a fireworks display on Nice's seafront Promenade des Anglais, injuring more than 300 people.

Four men and a woman have already been charged with being accomplices to murder by a terrorist group.

Prosecutor Francois Molins said that correspondence between the suspects and Bouhlel - shot dead by police during the attack - indicated they had been in on the plot.

The attack was claimed by the Islamic State in Iraq and Syria (ISIS) militant group.

However while Bouhlel had gruesome images on his computer related to the group, as well as its rivals Al-Qaeda, investigators have not turned up evidence of his sworn allegiance to the group.