French investigators have yet to find links between Bouhlel and the Islamic State group, which claimed responsibility for the carnage, Interior Minister Bernard Cazeneuve told France's RTL radio on Monday.

"We cannot exclude that an unbalanced and very violent individual" has been "through a rapid radicalisation, committed to this absolutely despicable crime," he said.

Did he work alone?

Police are searching for any accomplices to the attack, which appears to have been premeditated. They found a pistol, a larger gun, and a number of fake weapons and grenades in his vehicle after the attack.

It is believed he may have hired the lorry on Wednesday night and boarded it "in the hills of Nice" before driving down to the promenade, according to CCTV footage.

Seven people including a woman were in custody on Sunday night after the arrests earlier in the day of an Albanian couple suspected of aiding Bouhlel, described by the Islamic State of Iraq and the Levant (Isil) as one its “soldiers”.