French president Emmanuel Macron says his country is “under attack” from extremism after a woman was reportedly beheaded and two others killed at a church in Nice.

Shouting “Allahu Akbar” (God is Greatest), a man armed with a knife entered the Notre-Dame basilica, slitting the throat of the sexton, beheading an elderly woman, and badly wounding a third woman who escaped and later died, a police source told AAP.

About 4000 troops  – potentially rising to 7000 – are being deployed across the country to protect key French sites such as churches and schools as Mr Macron vowed not to give in to the “terrorist madness”.

France’s security alert has also been elevated to its highest level.

Police identified the alleged killer as 21-year-old migrant Brahim Aouissaoui, a Tunisian migrant who had recently entered France from Italy.

French forensics officers outside the Basilica of Notre-Dame de Nice. Photo: Getty

The latest horrific attack on the birthday of the Prophet Mohammed comes less than a fortnight after the beheading of school teacher Samuel Paty, who had used cartoons of the Muslim prophet in a civics class.

With Europe’s largest Muslim community, France has suffered a string of jihadist attacks in recent years, including bombings and shootings in Paris in 2015 that killed 130 people and a 2016 attack in Nice in which a militant drove a truck through a seafront crowd celebrating Bastille Day, killing 86.

Mr Macron visited the scene of the latest killings in the south of France, vowing to defend the country’s values.

“I say this with the outmost clarity — we will not give in to terrorism,” he said.

“Once again this morning, it was three of our compatriots that fell in Nice, and very clearly France is under attack.

Mr Macron said France had been attacked “over our values, for our taste for freedom, for the ability on our soil to have freedom of belief”.

“And I say it with lots of clarity again today: we will not give any ground.”

Muslim faithful from Marseille hold white flowers at the Notre-Dame de la Garde basilica in Marseille, south-eastern France. Photo: Getty

Within hours of the Nice attack, police killed another man who had threatened passers-by with a handgun in Montfavet, near the southern French city of Avignon.

Thursday’s attack, on the birthday of the Prophet Mohammed, came at a time of growing Muslim anger at France’s defence of the right to publish the cartoons.

Prime Minister Scott Morrison said Australia stood with France after the “terrible and disgraceful and disgusting attack”.

“It is just the most callous and cowardly and vicious act of barbarism by a terrorist and should be condemned in the strongest possible way,” Mr Morrisons said on 2GB radio in Sydney.

Mr Morrison has contacted the French president.

“The heartache that would be going across the French people today as it shudders through the rest of the world is hard to put into words,” Mr Morrison said.

Many world leaders have condemned the attack including the UK, the Netherlands, Italy, Spain, Saudi Arabia and Turkey, whose President Tayyip Erdogan earlier this week slammed Macron and France over displays of the Prophet Mohammed.

Turkish Presidential Communications Director Fahrettin Altun said Islam could not be used in the name of terrorism, adding: “We call on the French leadership to avoid further inflammatory rhetoric against Muslims and focus, instead, on finding the perpetrators of this and other acts of violence”.

A representative of the French Council for the Muslim Faith also condemned the attack.

“As a sign of mourning and solidarity with the victims and their loved ones, I call on all Muslims in France to cancel all the celebrations of the holiday of Mawlid.”

As police officers stand guard by the Notre-Dame de l’Assomption Basilica in Nice, some 4000 troops are deployed across France. Photo: Getty

The holiday is the birthday of the Prophet Mohammed, celebrated on Thursday.

The foreign ministry of Saudi Arabia, the birthplace of Islam, said “extremist acts” such as that in Nice “contravene all religions,” while stressing “the importance of avoiding all practices which generate hatred, violence and extremism”.

Other attacks in France

September 25, 2020 – Two people were stabbed and wounded in Paris near the former offices of the Charlie Hebdo satirical magazine, where Islamist militants carried out a deadly attack in 2015. A man originally from Pakistan was arrested over the attack.

October 3, 2019 – Mickael Harpon, a 45-year-old IT specialist with security clearance to work in the Paris police headquarters, killed three police officers and one civilian employee before being shot dead by police. He had converted to Islam about 10 years earlier.

March 23, 2018 – A gunman kills three people in southwestern France after holding up a car, firing on police and taking hostages in a supermarket, screaming “Allahu Akbar”. Security forces storm the building and kill him.

July 26, 2016 – Two attackers kill a priest and seriously wound another hostage in a church in northern France before being shot dead by French police. Francois Hollande, who was France’s president at the time, says the two hostage-takers had pledged allegiance to Islamic State.

July 14, 2016 – A gunman drives a heavy truck into a crowd celebrating Bastille Day in the French city of Nice, killing 86 people and injuring scores more in an attack claimed by Islamic State. The attacker is identified as a Tunisian-born Frenchman.

June 14, 2016 – A Frenchman of Moroccan origin stabs a police commander to death outside his home in a Paris suburb and kills his partner, who also worked for the police. The attacker told police negotiators during a siege that he was answering an appeal by Islamic State.

November 13, 2015 – Paris is rocked by multiple, near simultaneous gun-and-bomb attacks on entertainment sites around the city, in which 130 people are killed and 368 are wounded. Islamic State says it was responsible for the attacks. Two of the 10 known perpetrators were Belgian citizens and three others were French.

January 7-9, 2015 – Two Islamist militants break into an editorial meeting of satirical weekly Charlie Hebdo on January 7 and rake it with bullets, killing 12 people. Another militant kills a policewoman the next day and takes hostages at a supermarket on January 9, killing four before police shoot him dead.

-with AAP