World leaders are attending ceremonies commemorating the massacre 100 years ago of 1.5 million Armenians by Ottoman Turks.
The event, around the time of the First World War, is viewed by historians as genocide but modern Turkey, the successor to the Ottoman Empire, vehemently rejects the charge.
Russian president Vladimir Putin, French president Francois Hollande and other world leaders and dignitaries assembled this morning at the Tsitsernakaberd memorial complex in the Armenian capital, Yerevan.
Each leader walked along the memorial with a single yellow rose and put it into the centre of a wreath resembling a forget-me-not, a flower that was made the symbol of the commemoration.
Earlier, Turkey's president insisted his nation's ancestors had never committed genocide .
Addressing a meeting billed as an international peace summit, Recep Tayyip Erdogan said: "The Armenian claims on the 1915 events, and especially the numbers put forward, are all baseless and groundless.
"I say, we're ready to open our military archives. We have no fear, no worries on this subject. Our ancestors did not persecute."
Hundreds of Mr Erdogan's supporters also attended, boisterously cheering and applauding his words and giving the event the feel of a campaign rally six weeks before Turkey's elections.
The annual April 24 commemorations mark the day when some 250 Armenian intellectuals were rounded up in what is regarded as the first step of the massacres.
The massacres, deportations and forced marches began in 1915 as Ottoman officials worried that the Christian Armenians would side with Russia, its enemy in the war.
Speaking at the ceremony, Armenian president Serge Sarkisian expressed hope that recent steps to recognise the massacre as genocide will help "dispel the darkness of 100 years of denial".
He also welcomed Armenians from Turkey who were preparing to gather in Istanbul's Taksim Square to honour the dead, calling them "strong people who are doing an important thing for their motherland".
Elsewhere, Germany's parliamentary speaker said the event was genocide, adding that Germany's past makes it important to speak out.
Norbert Lammert told Parliament: "We Germans cannot lecture anyone about dealing with their past, but we can through our own experiences encourage others to confront their history, even when it hurts."
"We will never forget the tragedy that your people went through," Mr Hollande said.
France is home to a sizeable Armenian community. Among the French Armenians at Yerevan was 90-year old singer Charles Aznavour who was born in Paris to a family of massacre survivors.
Mr Putin used his speech to warn of the dangers of nationalism as well as "Russophobia" in a clear dig at the West-leaning government in Ukraine.