In a statement likely to strain diplomatic ties with Turkey, Pope Francis referred to the 20th century mass killings of Armenians as the first genocide of the 20th century during a mass to commemorate the 100th anniversary of the killings.

“In the past century our human family has lived through three massive and unprecedented tragedies,” Francis said during mass in Saint Peter’s Basilica on Sunday morning. “The first, which is widely considered ‘the first genocide of the 20th century’, struck your own Armenian people,” he said.

Over 1.5 million Armenians perished under the Ottoman Empire during World War I.  Armenians have been fighting for years to receive recognition that the event was indeed a genocide. Turkey has ardently insisted that the event was not a genocide, and that the deaths of the Christian Armenians were merely a part of the partisan fighting.

Francis referred to the tragedy as a “senseless slaughter,” stating that it is important to keep the memory of the genocide alive.

“It is necessary, and indeed a duty, to honor their memory, for whenever memory fades, it means that evil allows wounds to fester,” Francis said. “Concealing or denying evil is like allowing a wound to keep bleeding without bandaging it.”

The Pope also recalled  other mass killings of the 20th century, such as  those in Cambodia, Rwanda, Burundi and Bosnia. “It seems that humanity is incapable of putting a halt to the shedding of innocent blood,” he added.

Patriarch of the Armenian Catholic Church, His Beatitude Nerses Bedros XIX, His Holiness Karekin II, Catholicos of All Armenians, and His Holiness Aram I, Catholicos of the Holy See of Cilicia of the Armenian Apostolic Church were all in attendance during the mass.

Turkey has yet to respond to the statement by Pope Francis, but it is unlikely they will take kindly to the Vatican referring to the deaths of the Christian Armenians as a “genocide.”