It was "homicidal folly, hatred, terrorism, and attacks against peace", said Catholic Church spokesman Fr Federico Lombardi.
He said Pope Francis condemned the incident in which 84 people died when a terrorist drove a truck through crowds celebrating Bastille Day in Nice.
France has declared three days of national mourning following the atrocity, which comes after attacks in November in Paris in which 130 died and in January 2015 that killed 17.
Pope Francis followed the events during the night "with the greatest concern," added Fr Lombardi.
The leader of Catholics in England and Wales, Cardinal Vincent Nichols, tweeted his "heartfelt prayers" in the aftermath of the attack which he said was a "deep loss".
Scotland's Archbishop of St Andrews and Edinburgh, Leo Cushley, who is in Lourdes, said he prayers were with those involved.
Cardinal Pietro Parolin, the Vatican's Secretary of State, said it was "blind violence" and that Pope Francis shared in the grief.
Eyewitnesses said the Nice attacker - reported to be 31-year-old Mohamed Lahouaiej Bouhlel, a man of French-Tunisian origin who was known to the authorities for anti-social behaviour - swerved from side to side to kill as many people as possible as he drove for a mile along the Promenade des Anglais on the seafront of the city on the French Riviera.
He is said to have pulled a gun from the cab as part of the premeditated attack before being shot dead by police, with people fleeing into the sea in a bid to escape.
Theresa May, the new Prime Minister, condemned the "horrifying" terror attack.
