Muslims across France attended Catholic Mass on Sunday to show their solidarity and compassion in the wake of the brutal murder of a French priest by two teenagers who claimed to be acting in the name of the Islamic State.

"Solidarity and condolences," Anouar Kbibech, the head of the French Council of the Muslim Faith wrote on Twitter. "Call to national unity."

The Associated Press reported that a few dozen Muslims congregated at the Gothic cathedral in Rouen where Reverend Jacques Hamel, 85, had his throat slit on Tuesday.

Among the parishioners in Rouen was a nun who was taken hostage at Hamel's church. According to AP, she shook hands and embraced Muslim churchgoers. Muslims also revealed a banner outside the church, with the words "Love for all. Hate for none."

Other gestures of solidarity were reported elsewhere in France, such as in Paris, at the Notre-Dame Cathedral, and in Nice, where the French Riviera city's top imam Otaman Aissaoui reportedly led a delegation to mass. Nice, too, was recently shaken by an IS-linked incident after a man plowed through a Bastille Day crowd who had gathered to watch the fireworks, killing 85 and injuring 435 (including many Muslims.)

"Being united is a response to the act of horror and barbarism," Aissaoui told al-Jazeera.

Also on Sunday, Prime Minister Manuel Valls called for a new "pact" with France's Muslim community. "Islam has found its place in the Republic" Valls wrote, "Contrary to the repeated attacks of populists on the right and far-right." Valls also stressed his condemnation of that "intolerable rejection of Islam and Muslims."

The show of solidarity also comes as Muslim community leaders put up a united front in their refusal to bury one of the teens who murdered the priest.

Gestures of solidarity from Muslim leaders also happened in Italy, the European country with the biggest Catholic population.

Abdullah Cozzolino, the secretary general of Italy's Islamic Confederation, spoke from the altar of the St Gennaro chapel near Naples' Duomo cathedral, CBS reported. Cozzolino stressed the need for "dialogue, more affirmation of shared values of peace, of solidarity, of love, out of respect for our one God, merciful and compassionate."

Like France, Italy is ramping up surveillance of its Muslim communities.

In a sermon on Friday, Mohammed ben Mohammed, a member of the Union of Islamic Communities in Italy, defended the country's mosques as places of worship.