Pope Francis has angered the Turkish government by describing the mass-murders of up to 1.5million Armenians in 1915 as 'the first genocide of the 20th century'.
The pontiff made the comments at a 100th anniversary Mass on Sunday, prompting Turkey to summon the Holy See's ambassador in Ankara in protest.
Turkey told the Vatican ambassador it was 'deeply sorry and disappointed' in Pope Francis, adding that his comments had caused a 'problem of trust'
While Turkey accepts that many Armenians died in clashes with Ottoman soldiers beginning in 1915, when Armenia was part of the empire ruled from Istanbul, it denies that the victims reached the estimated 1.5million and that this amounted to genocide.
Today was the first time a pope has publicly used 'genocide' to describe the massacre, although it is a term used by many European and South American governments.
In 2001, Pope John Paul II and Armenian Apostolic Church Supreme Patriarch Kerekin II called it 'the first genocide of the 20th century' in a joint written statement.
Francis, who has disregarded many aspects of protocol since becoming pope two years ago, uttered the phrase during a private meeting at the Vatican with an Armenian delegation in 2013, prompting a strong protest from Ankara.
As the archbishop of Buenos Aires before becoming the leader of the world's 1.2 billion Catholics, Jorge Maria Bergoglio had already publicly characterised the mass killings as genocide.
At the start of the Armenian rite Mass in St. Peter's Basilica, Pope Francis described the 'senseless slaughter' of 100 years ago as 'the first genocide of the 20th century', which was followed by 'Nazism and Stalinism'.
'It is necessary, and indeed a duty, to honour their memory, for whenever memory fades, it means that evil allows wounds to fester. Concealing or denying evil is like allowing a wound to keep bleeding without bandaging it!' he said.
Francis's comments were also published by Armenian President Serzh Sargyan's office on Sunday.
'We are deeply grateful to His Holiness Pope Francis for the idea of this unprecedented liturgy ... which symbolizes our solidarity with the people of the Christian world,' Sargyan said in a speech at a Vatican dinner on Saturday evening.
After Francis's remarks on Sunday, Turkey swiftly summoned the Vatican's ambassador in Ankara to protest and seek an explanation.
'The pope's statement which is far from historic and legal truths is unacceptable. Religious positions are not places where unfounded claims are made and hatred is stirred,' Foreign Minister Mevlut Cavusoglu tweeted.
The Foreign Ministry in Ankara later 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.
Francis also urged reconciliation between Turkey and Armenia, and between Armenia and Azerbaijan over the disputed Caucasus mountain region of Nagorno-Karabakh.
The appeal came in a letter handed out during a meeting after the Mass to Sargyan and the three most important Armenian church patriarchs present.
