YEREVAN, Armenia - The Armenian Church prepares Thursday to canonise up to 1.5 million Armenians massacred in the Ottoman Empire amid tensions over Turkey's refusal to recognise the killings as genocide.
The ceremony - that could become the biggest canonisation service in history - comes ahead of emotional commemorations expected to see millions including heads of state mark a hundred years since the start of the tragedy on Friday.
"On April 23... the canonisation service for the Martyrs of the Armenian Genocide will be offered," said the Armenian Apostolic Church, calling on all Armenians for the "prayerful participation in this historic event".
The service will be held Thursday evening in Armenia's main church, Echmiadzin, an austere 4th-century edifice believed to be the Christian world's oldest cathedral.
After the ceremony to be led by Catholicos of All Armenians, Karekin II, bells will chime in Armenian churches across the world and a minute of silence will be observed.
In canonising the genocide victims, "the Church only recognises what happened: that is, the genocide", Karekin II said ahead of the event which Christian Today said could become "the biggest saint-making service in history".
Ex-Soviet Armenia and the huge Armenian diaspora worldwide have battled for decades to get the World War I massacres at the hands of the Ottoman forces between 1915 and 1917 recognised as a targeted genocide.
But modern Turkey - the successor to the Ottoman empire - has refused to do so.
Ankara says that 300,000 to 500,000 Armenians and at least as many Turks died in civil - rather than religious - strife when Armenians rose up against their Ottoman rulers and sided with invading Russian troops.
On Friday, hundreds of thousands are expected to join a procession to a hilltop memorial in the Armenian capital Yerevan carrying candles and flowers to lay at the eternal flame at the centre of a monument commemorating the mass murder.
In Paris, Los Angeles and other cities, members of the Armenian diaspora - that came to existence as a result of the slaughter - will also hold commemorations.
Russian strongman Vladimir Putin and French President Francois Hollande are expected to be among a handful of world leaders to travel to Armenia for the commemorations, but others are shying away for fear of upsetting Ankara.
In the run-up to the ceremonies Turkey kicked up a diplomatic storm, condemning growing "racism" in Europe.
On Wednesday Turkey recalled its ambassador to Vienna in protest against the Austrian parliament's decision to call the massacre "genocide."
Earlier this month Ankara recalled its envoy to Vatican after Pope Francis described the killings as "the first genocide of the 20th century."
More than 20 nations - including France and Russia - have so far recognised the Armenian genocide, a definition supported by numerous historians.