VATICAN CITY — Pope Francis on Sunday marked the 100th anniversary of the slaughter of Armenians by calling the massacre by Ottoman Turks “the first genocide of the 20th century” and urging the international community to recognize it as such.

Turkey responded by recalling its ambassador and accusing Francis of spreading hatred and “unfounded claims.”

Francis issued the pronouncement during a Mass in St. Peter’s Basilica commemorating the centenary that was attended by Armenian church leaders and President Serge Sarkisian, who praised the pope for calling a spade a spade and “delivering a powerful message to the international community.”

“The words of the leader of a church with 1 billion followers cannot but have a strong impact,” he said.

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, denies a genocide took place. It has insisted that the toll has been inflated and that those killed were victims of civil war and unrest.

Francis said it was his duty to honor the memory of the innocent men, women and children who were “senselessly” murdered by Ottoman Turks.

“Concealing or denying evil is like allowing a wound to keep bleeding without bandaging it,” he said.

He said similar massacres are underway against Christians who, because of their faith, are “publicly and ruthlessly put to death — decapitated, crucified, burned alive — or forced to leave their homeland,” a reference to the Islamic State group’s assault against Christians in Iraq and Syria.

Francis called on the world community, heads of state and international organizations to recognize the truth of what transpired to prevent such “horrors” from repeating themselves.

Turkey has lobbied to prevent countries, including the Holy See, from recognizing the Armenian massacre as genocide and reacted strongly to Francis’ declaration.

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

The Foreign Ministry summoned the Vatican’s envoy in Ankara, and then announced it was recalling its own ambassador to the Vatican for consultations.

Several European countries recognize the massacres as genocide, though Italy and the United States, for example, have avoided using the term officially, given the importance they place on Turkey as an ally.

Francis’ willingness to rile Ankara showed once again that he has few qualms about taking diplomatic risks for issues close to his heart. And the massacre of Armenians is indeed close to the Vatican’s heart given that Armenia is held up as the first Christian nation, dating from 301.

Francis is not the first pope to call the massacre a genocide. St. John Paul II wrote in a 2001 joint declaration with the Armenian church leader, Karekin II, that the deaths were considered “the first genocide of the 20th century.”

But the context of Francis’ pronunciation was different: in St. Peter’s during an Armenian rite service with the Armenian church and state leadership in attendance on the 100th anniversary of the slaughter. His call for international acknowledgment went beyond what John Paul had written.