VATICAN CITY -- Four leading French imams and the Vatican issued a joint declaration Thursday denouncing the Paris newspaper massacre and warning that the world is a dangerous place without freedom of expression, but urged the media to be respectful of religions.

The Vatican's office for interreligious dialogue said the four Muslim spiritual leaders, who were visiting the Vatican this week, joined Pope Francis in condemning the attack and urging all believers to show friendship and solidarity to the victims.

The declaration, issued in French, stressed that dialogue among faiths was the only way to eliminate prejudice.

"In these circumstances, we should recall that the world is in danger without freedom of expression," it said. But it added: "Considering the impact of the media, the (signatories) invite media leaders to provide information that respects religions, their followers and their practices, thus promoting a culture of encounter."

In addition to French Cardinal Jean-Louis Tauran, who heads the pontifical council, the signatories included Djelloul Seddiki, head of the Paris Mosque, Tareq Oubrou, director of the Bordeaux mosque, Azzedine Gaci of the Villeurbanne mosque and Mohammed Moussaoui, president of the Union of Mosques in France.

Francis, meanwhile, celebrated a Mass in memory of the victims Thursday morning, decrying the "human cruelty" it showcased. Francis asked for prayers for the victims and said "we also ask for those who are cruel so that the Lord may change their heart."

Francis also sent a one-line tweet from his (at)Pontifex handle: .PrayersforParis.

The Vatican has sought to mend relations with Islam that were initially strained under Pope Benedict XVI. Francis has a long history of promoting interfaith dialogue.

On Thursday, he met with a delegation of Yazidis, the religious minority that has been brutally targeted by Islamic State group militants in northern Iraq.

The Vatican said the Yazidi delegation briefed Francis on the atrocities against their people -- about 5,000 women enslaved by IS -- and thanked the pope for his support.