The Turkish president has sharply criticised Pope Francis for describing the mass killing of Armenians under Ottoman rule in WW1 as “genocide”.
Recep Tayyip Erdogan said he condemned the Pope and warned him to “not repeat this mistake”.
Turkey rejects the use of the term genocide to describe the killings, arguing it was a civil war in which both sides died.
It is calling for a joint study by historians of what happened.
Turkey recalled its envoy to the Vatican after Pope Francis made the comments on Sunday at a Mass at St Peter’s Basilica, attended by the Armenian president and the head of the Armenian Apostolic Church, Karekin II.
The Pope said that humanity had lived through “three massive and unprecedented tragedies” in the last century.
“The first, which is widely considered the first genocide of the 20th Century, struck your own Armenian people,” he said, in a form of words used in a declaration by Pope John Paul II in 2001.
Pope Francis also referred to the crimes “perpetrated by Nazism and Stalinism”.
But Mr Erdogan said on Tuesday that when political or religious leaders played the role of historians, what resulted was “delirium, not fact”.
“Hereby, I want to repeat our call to establish a joint commission of historians and stress we are ready to open our archives. I want to warn the Pope to not repeat this mistake and condemn him.”
The issue is always sensitive in Turkey but particularly so in the run-up to the 100th anniversary of the killings next week and a general election in June, in which the country’s leaders are trying to shore up their nationalist support, says the BBC’s Mark Lowen in Istanbul.
Last year, Mr Erdogan offered “condolences” to the families of those who died and called the events “inhumane”.
It was seen as a step towards reconciliation but was rejected by Armenia for avoiding the word “genocide”.
While most non-Turkish scholars and more than 20 countries regard what happened as genocide, Turkey rejects use of the word, maintaining that many of the dead were killed in clashes during World War One.
Many of the victims were civilians deported to barren desert regions where they died of starvation and thirst. Thousands also died in massacres.
Armenia says up to 1.5 million people were killed but Turkey says the number was far smaller.