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. An estimated 1.5 million died in the massacres, deportations and forced marches that began in 1915 as Ottoman officials worried that the Christian Armenians would side with Russia, its enemy in the World War I.
The event is widely viewed by historians as genocide but modern Turkey, the successor to the Ottoman Empire, vehemently rejects the charge, saying that the toll has been inflated, and that those killed were victims of civil war and unrest. On the eve of the centennial, Turkish President Recep Tayyip Erdogan insisted that his nation's ancestors never committed genocide.
Russian President Vladimir Putin, French President Francois Hollande and other dignitaries assembled Friday morning at the Tsitsernakaberd memorial complex in the capital, Yerevan.
Each leader walked along the memorial with a single yellow rose and put it into the center of a wreath resembling a forget-me-not, a flower that was made the symbol of the commemoration.
"We will never forget the tragedy that your people went through," 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.
Russian President Vladimir 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.
Earlier this month, Turkey recalled its ambassadors to Vienna as well as the Vatican after Austria and Pope Francis described the killings as genocide. The European Parliament has also triggered Turkey's ire by passing a non-binding resolution to commemorate "the centenary of the Armenian genocide."
Armenian President Serge Sarkisian expressed hope that recent steps to recognize the massacre as genocide will help "dispel the darkness of 100 years of denial."
Armenians and Turks planned to march in Istanbul's main square to remember the Armenian intellectuals who were rounded up in the city 100 years ago and to urge the government into recognizing genocide. A small nationalist group planned a protest denouncing the accusations of genocide.
Sarkisian welcomed the rally in Taksim Square to honor the dead, calling them "strong people who are doing an important thing for their motherland."
Turkish Prime Minister Ahmet Davutoglu earlier this week issued a message of condolence to the descendants of the victims, without calling the killings genocide.
"We respect the pain experienced by our Armenian brothers," Bozkir said. "We are in no way opposed to the commemoration of this pain... We felt indebted to attend this service."