In a statement released by his Spokesperson, António Guterres extended his condolences to the families of the victims, and reaffirmed “the solidarity of the United Nations with the people and the Government of France.”

A lone attacker armed with a knife entered the Notre Dame Basilica in the city centre at around 9am, according to news reports. A man and a woman died at the scene, while another woman died from her injuries. The attacker was injured after being shot by police and taken to hospital.

French authorities are treating it as a terrorist incident.

Attacks in France, Saudi Arabia

The deadly attack in Nice, was not the only violent incident to take place on Thursday, in the wake of a strong reaction in France, led by President Macron, to the beheading of a teacher near Paris nearly two weeks ago.

That attack was reportedly carried out in response to the re-publication of satirical caricatures of the Prophet Muhammed, in the Charlie Hebdo magazine.

A man was shot dead on Thursday near the southern French city of Avignon, after reportedly threatening police with a handgun, and according to news reports, a guard outside the French consulate in Jeddah, Saudi Arabia, was attacked and wounded. The suspect was detained.

Following the killings in Nice, French police have launched a murder inquiry, with President Macron denouncing it as an “Islamist terrorist attack”, and the national security alert system has been raised to its highest level.

In the wake of the killing of school teacher Samuel Paty, and President Macron’s defence of the publication of the cartoons, there have been protests in some Muslim nations at what is being perceived as an anti-Muslim backlash, and calls for a boycott of French goods, including from Turkish President, Recep Tayyip Erdogan.

‘Intolerable and utterly unjustifiable’ attacks, but mutual tolerance needed

In a statement issued in response to the killings in Nice, the senior UN official who oversees the protection of religious sites and advocates for religious tolerance, Miguel Aìngel Moratinos, strongly condemned the “barbaric attack”, stressing that any attacks targeting civilians, including worshippers, were “intolerable and utterly unjustifiable, whenever, wherever and by whomsoever committed.”

But the High-Representative for the UN Alliance of Civilizations (UNAOC), also noted that such “outrageous crimes should not dissuade us from working together to promote mutual respect and peace globally, as one humanity.”

In an earlier statement released on Wednesday, he said that he was following the fallout from “growing tensions and instances of intolerance” triggered by the publication of the satirical caricatures of the Prophet Muhammed, with “deep concern”.

He pointed out that the re-publication of the images has been viewed as “insulting and deeply offensive” by many Muslims.

“The inflammatory caricatures have also provoked acts of violence against innocent civilians who were attacked for their sheer religion, belief or ethnicity.

“The High-Representative stresses that insulting religions and sacred religious symbols, provokes hatred and violent extremism leading to polarization and fragmentation of society”, said the statement. “He calls for mutual respect of all religions and beliefs and for fostering a culture of fraternity and peace.”

Mr. Moratinos noted that “the freedom of religion or belief and the freedom of expression are interdependent, interrelated and mutually re-enforcing rights rooted in the articles 18 and 19 of the Universal Declaration of Human Rights (UDHR), noting that upholding and protecting these fundamental rights is the primary responsibility of Member States.

Respect all religions

“At the same time, freedom of expression should be exercised in a way that fully respects the religious beliefs and tenets of all religions.”

He said violence was never a justifiable or acceptable response to acts of intolerance on the basis of religion or belief.

The High-Representative is in charge of implementing a UN Plan of Action and Strategy on Hate Speech, a guide to help fight hate speech, racism and discrimination.

The UNAOC was created fifteen years ago to bolster conflict prevention through the promotion of intercultural and interreligious dialogue and build bridges of understanding between different cultures and religions.