Three people died in a knife attack in Nice, France. French president Emmanuel Macron said was an “Islamist terrorist attack”.
Mr Macron said France would not surrender its core values after visiting the Notre-Dame basilica in the southern city. Thousands of troops are being deployed to protect churches and schools.
In Nice, one elderly victim was “virtually beheaded”, officials said. Another woman and a man also died.
A suspect was shot and detained.
Anti-terror prosecutors have opened an investigation into the attack and France has raised its national security alert to its highest level.
French media are quoting sources close to the investigation as saying the attacker was a 21-year-old Tunisian migrant, however the authorities have not provided any details.
Nice Mayor Christian Estrosi spoke of “Islamo-fascism” and said the suspect had “repeated endlessly ‘Allahu Akbar’ (God is greatest)”.
Two other attacks took place on Thursday, one in France and one in Saudi Arabia.
A man was shot dead in Montfavet near the southern French city of Avignon after threatening police with a handgun.
A guard was attacked outside the French consulate in Jeddah in Saudi Arabia. A suspect was arrested and the guard taken to hospital.
The murder has heightened tensions in France and the government’s attempt to crack down on radical Islam has angered Turkey and other countries.
Turkish President Recep Tayyip Erdogan was among those calling for a boycott of French goods.
The situation worsened after a cartoon on Mr Erdogan appeared in the satirical magazine Charlie Hebdo.
Four years ago Nice was the scene of terrorist attack, when a Tunisian drove a truck into crowds celebrating Bastille Day on 14 July, killing 86 people.