"France has been hit yet another time by a terrorist attack of the utmost severity", the council said in a statement, adding that the "odious terrorist act took aim at our country on the very day of its national holiday, a day which celebrates liberty, equality and fraternity". The state of emergency has been extended.
May, who took over as prime minister on Wednesday with the job of steering Britain out of the European Union, said her deputy national security adviser would chair the review.
"And, as I say, the threat level here is already at a level that says a terrorist attack is highly likely".
The French Tunisian man, 31, drove the terror-lorry for a mile along the Promenade des Anglais before exiting the huge rig and opening fire on more terrified people. The official said weapons and grenades were found inside the 25-tonne, unmarked articulated truck. Hollande said it was not immediately clear whether the driver had accomplices.
The truck driver has been identified as French born in Tunisia.
Five to ten minutes after the fireworks ended, police cars rushed past him and an influx of people began running in his direction on the Promenade. "You can see wreckage all along the way: a body, bicycles, street lamps and debris everywhere", he said.
"We all just knew that we had to run for our lives". A woman was there, she lost her son. Photos showed a truck with around 20 bullet holes. He urged residents to stay indoors.
France's Interior Ministry said 84 people were killed in the attack.
On March 22, suicide bombers killed 32 victims in the Brussels Airport and subway.
Prime Minister Theresa May says Britain stands shoulder to shoulder with France after the Nice attack that killed over 80 people and was reviewing whether the United Kingdom needed to do more to boost its own security.
The attacker had been convicted of misdemeanor crimes but had no known ties to terrorists, the officials told the AP. Hollande announced a three-month extension to the state of emergency imposed after the November 13 attacks on Paris that killed 130 victims.
Earlier Thursday, thousands of people had gathered in Paris to watch the traditional Bastille Day military parade and fireworks displays were held across France.
"All these bodies and their families ... they spent hours on the ground holding the cold hands of bodies dismembered by the truck".
"The beach attendants were first on the scene".
A journalist with the Nice Matin newspaper reported from the scene that there was "a lot of blood".
While claiming the responsibility of the Paris terror attacks previous year ISIS termed the French capital "the capital of prostitution and vice."The terrorist group also stated that France and "all nations following in its path" are "at the top of the target list for the Islamic State".
Landry noted that the tone in Nice today isn't one of panic, just sadness.