France raises security threat to highest level: Prime Minister Castex

France has raised the security alert for French territory to the highest level after the knife attack in the city of Nice, Prime Minister Jean Castex said on Thursday.

Castex also told French National Assembly that the government’s response to the attack would be firm and implacable.

Read more: France knife attack: Woman beheaded in Nice church, two others dead, several injured

An attacker with a knife killed three people, including a woman who was decapitated, at a church in the French city of Nice on Thursday, police said, in an incident the city’s mayor described as terrorism.

Mayor Christian Estrosi said on Twitter the knife attack had happened in or near the city’s Notre Dame church and that police had detained the attacker.

Estrosi said the attacker had shouted the phrase “Allahu Akbar”, or God is greatest.

The attack comes while France is still reeling from the beheading earlier this month of French middle school teacher Samuel Paty by a man of Chechen origin.

Read more: Beheading in Nice church the latest in France’s recent history of attacks