VATICAN CITY: Pope Francis on Sunday called the slaughter of Armenians by Ottoman Turks “the first genocide of the 20th century” and urged the international community to recognize it as such, sparking a diplomatic rift with Turkey.

Turkey, which has long denied a genocide took place, immediately summoned the Vatican ambassador to complain and promised a fuller official response.

“The pope’s statement which is far from historic and legal truths is unacceptable,” Foreign Minister Mevlut Cavusoglu tweeted. “Religious positions are not places where unfounded claims are made and hatred is stirred.”

Francis, who has close ties to the Armenian community from his days in Argentina, defended his pronouncement by saying it was his duty to honor the memory of the innocent men, women and children who were “senselessly” murdered by Ottoman Turks 100 years ago this month.

“Concealing or denying evil is like allowing a wound to keep bleeding without bandaging it,” he said at the start of a Mass in the Armenian Catholic rite in St. Peter’s Basilica honoring the centenary.

In a subsequent message directed to all Armenians, Francis called on all heads of state and international organizations to recognize the truth of what transpired and oppose such crimes “without ceding to ambiguity or compromise.”

Historians estimate that up to 1.5 million Armenians were killed by Ottoman Turks around the time of World War I, an event widely viewed by scholars as the first genocide of the 20th century.

Turkey, however, has insisted that the toll has been inflated, and that those killed were victims of civil war and unrest, not genocide. It has fiercely lobbied to prevent countries, including the Holy See, from officially recognizing the Armenian massacre as genocide.

Turkey’s embassy to the Holy See canceled a planned news conference for Sunday, presumably after learning that the pope would utter the word “genocide” over its objections. Instead, the Foreign Ministry in Ankara issued a statement conveying its “great disappointment and sadness.” It said the pope’s words signaled a loss in trust, contradicted the pope’s message of peace and was discriminatory because Francis only mentioned the pain of Christians, not Muslims or other religious groups.

Reaction to the pope’s declaration on the streets in Istanbul was mixed. Some said they supported it, but others did not agree.

“I don’t support the word genocide being used by a great religious figure who has many followers,” said Mucahit Yucedal, 25. “Genocide is a serious allegation.”

Francis’ words had immediate effect in St. Peters, where the head of the Armenian Apostolic Church, Aram I thanked Francis for his clear condemnation and recalled that “genocide” is a crime against humanity that requires reparation.