Attacker shouting "Allahu Akbar" beheads an elderly woman praying inside French church, kills two others.

One woman was reportedly decapitated and two other people were stabbed to death on Thursday following a knife attack at a church in the French city of Nice that also left several others wounded, according to multiple reports.

The suspect, believed to be acting alone, was injured during his arrest and was taken to a local area hospital, police said.

An investigation was opened into an attack by the French anti-terrorism prosecutor's office, reports said. Images on French media showed the neighborhood locked down and surrounded by police and emergency vehicles.

Prime Minister Jean Castex said the country's threat level will be raised to its maximum after the attack. He also told the French National Assembly that the government's response to the attack would be firm and implacable.

Mayor Christian Estrosi suggested that the Thursday morning attack seemed to be terror-related, although a motive is unclear at this time. Estrosi said the attacker shouted "Allahu akbar!" -- or "God is most great" in Arabic -- repeatedly as police apprehended him and that "the meaning of his gesture left no doubt."

"Enough is enough," Estrosi told local reporters, according to Reuters. "It's time now for France to exonerate itself from the laws of peace in order to definitively wipe out Islamo-fascism from our territory."

He added that two people were killed inside the city's Notre Dame Basilica and a third person who escaped to a nearby bar later died.

Thursday's incident marked the third attack in France in less than two months since a terrorism trial opened in September related to the January 2015 killings at the satirical newspaper Charlie Hebdo and a kosher supermarket.

The attack at the church also happened less than a half a mile from the site in 2016 where another attacker plowed a truck into a Bastille Day crowd, killing dozens.

Thursday also marked the Prophet Muhammed's birthday.

European Commission President Ursula von der Leyen was quick to condemn the "heinous" attack in France and pledged solidarity in Europe "in the face of barbarism and fanaticism."

"I condemn the odious and brutal attack which has just taken place in Nice and am wholeheartedly with France. My thoughts are with the victims of this heinous act," she said in a statement. "The whole of Europe stands in solidarity with France. We remain united and determined in the face of barbarism and fanaticism."

The incident comes as France is currently under alert for Islamic extremist acts. It occurred nearly two weeks after a French middle school teacher, Samuel Paty, was beheaded by a man of Chechen origin near Paris.

The 18-year-old suspect, who was killed after he didn't respond to requests to drop his weapon, had said he wanted to punish Paty for showing pupils cartoons of the Prophet Mohammad in a civics lesson on free speech, Reuters reported.

Those caricatures were published by Charlie Hebdo and cited by the men who gunned down the newspaper's editorial meeting in 2015.

In September, a man who had sought asylum in France attacked bystanders outside Charlie Hebdo's former offices with a butcher knife.

The lower house of parliament suspended a debate on France's new virus restrictions and held a moment of silence Thursday for the victims. The prime minister rushed from the hall to a crisis center overseeing the aftermath of the Nice attack. French President Emmanuel Macron was headed to Nice later in the day.

About 154 miles away from Nice, French police on Thursday shot a man dead in Montfavet, near the city of Avignon in the south of France, for allegedly threatening a passerby with a handgun, Reuters reported, citing local media reports. According to French radio station Europe 1, the man had yelled, "Allahu Akbar."

The attacks come as France is set to begin a four-week lockdown on Friday amid a second surge of coronavirus infections.

Tensions have been rising between France and the Muslim world, which considers cartoons of the Prophet Muhammed blasphemous.

Images of the prophet have been widely displayed in marches and protests since Paty's slaying, as French officials and citizens alike reassert their freedom of expression. France has also since expelled 231 foreigners for suspected Islamic extremist beliefs, prompting Turkish President Recep Tayyip Erdogan and others in the Muslim world to accuse Macron of promoting an "anti-Islam agenda"

An estimated six million Muslims live in France, the largest population in Western Europe, which has created increasing challenges in the republic formed on strict secular principles known as "laïcité." In the eulogy at Paty's funeral, Macron defended France's secularism and vowed that the country would not give up its liberties or its cartoons.

"We will continue, professor. We will defend the freedom that you taught so well and we will promote secularism, we will not renounce caricatures, drawings, even if others retreat," Macron said earlier this month. "We will continue the fight for freedom and the freedom of which you are now the face."

Wednesday's edition of Charlie Hebdo also sparked furor for including a caricature of Erdogan in his underwear lifting up a Muslim woman's skirt. The Turkish president called the satirical image a "grave insult to my prophet" and renewed calls for a boycott of French goods in the Middle East.

A Saudi man was also arrested Thursday in the city of Jiddah for allegedly using a "sharp tool" to stab and slightly wound a guard at the French consulate, Reuters reported, citing Saudi state TV. France alerted its citizens to be on "high alert."

The Kremlin responded Thursday to the recent beheadings in France, saying it was unacceptable to kill people, but also wrong to insult the feelings of religious believers, according to Reuters.

Macron delivered a speech before the teacher was killed outlining a legislative proposal to fight what he described as "Islamic separatism," arguing Muslims in France risked forming a "counter-society." Macron defined Islam as "a religion that is in crisis today all over the world" and said the proposal, if approved by Parliament, would aim "to build an Islam in France that can be compatible with the Enlightenment."

The diplomatic dispute with Erdogan also comes as tensions between NATO allies France and Turkey have intensified in recent months over issues that include the fighting in Syria, Libya and Nagorno-Karabakh, a region within Azerbaijan that is controlled by ethnic Armenian separatists. Macron has accused Turkey of flouting its commitments by ramping up its military presence in Libya and bringing in jihadi fighters from Syria.