The southern French city of Nice was in mourning on Friday for the three people stabbed to death in a suspected jihadist attack at a church.
A makeshift memorial has been set up outside the Notre-Dame basilica, where people have placed flowers and lit candles for the victims.
French President Emmanuel Macron said Thursday’s stabbings were an “Islamist terrorist attack”.
He is to hold an emergency meeting with senior ministers on Friday.
Meanwhile, security has been stepped up at places of worship and schools across France following two similar attacks within two weeks. Earlier this month a teacher was beheaded in a Paris suburb after showing controversial cartoons of the Prophet Muhammad to some of his pupils.
Mr Macron’s subsequent defence of the right to publish the cartoons has stoked anger in several Muslim-majority countries.
Following the latest attack, police shot and wounded the suspected knifeman, identified as a 21-year-old Tunisian who had only recently arrived in Europe. He is said to be in a critical condition in hospital.
What do we know about the suspect?
Police sources named the man as Brahim Aouissaoui. Prosecutors said he had arrived by boat on the Italian island of Lampedusa as a migrant last month and after quarantining had been ordered to travel on.
He arrived in Nice by train and had no papers except for a Red Cross document from Italy, investigators said. A Tunisian official said he had not been listed as a suspected militant.
Speaking at the family home near the Tunisian port city of Sfax, Brahim Aouissaoui’s older brother, Yassin, described him as “a friendly person” who “never showed extremism”.
“He respected all other people and accepted their differences,” he told Reuters.
“He did not tell us [that he planned to leave Tunisia] and we were surprised when he told us he had reached Italy.”
Witnesses said the attacker repeatedly shouted “Allahu Akbar” (God is greatest) before being shot by police.
A Koran, two telephones and a 30cm (12-inch) knife were found on him, said French chief anti-terrorist prosecutor Jean-François Ricard.
“We also found a bag left by the attacker. Next to this bag were two knives that were not used in the attack,” he added.
In another development, a 47-year-old man believed to have been in contact with the suspect was detained by police late on Thursday, French media reported.
What has the official reaction been?
On Friday, Interior Minister Gerald Darmanin said France was “at war” with the political ideology of militant Islamism.
“We are at war… against an enemy who is both an internal enemy and an external enemy, an ideology because we are not at war against a religion,” he said. “We are at war against an ideology, Islamist ideology.”
Speaking after visiting Nice, Mr Macron told reporters: “If we are attacked once again it is for the values which are ours: freedom, for the possibility on our soil to believe freely and not to give in to any spirit of terror.
“I say it with great clarity once again today: we won’t surrender anything.”
He said the number of soldiers being deployed to protect public places – such as churches and schools – would rise from 3,000 to 7,000.
France has raised its national security alert to the highest level.