Ceremonies are being held in Armenia and around the world to mark the centenary of the start of mass killings of Armenians byOttoman Turks.
The presidents of France and Russia joined other leaders for the memorial in the Armenian capital, Yerevan.
Armenia says up to 1.5 million people died, a figure disputed by Turkey.
Turkey strongly objects to the use of the term genocide to describe the killings and the issue has soured relations between the nations.
Turkey accepts that atrocities were committed but argues there was no systematic attempt to destroy the Christian Armenian people. Turkey says many innocent Muslim Turks also died in the turmoil of war.
A memorial service was held in Turkey on Friday and its prime minister, Ahmet Davutoglu, said the country would "share the pain" of Armenians. But he reiterated Turkey's stance that the killings were not genocide.
Turkey is on Friday also hosting ceremonies to mark the 100th anniversary of the start of the Battle of Gallipoli.
However, the actual fighting there began on 25 April, and Armenian President Serzh Sargsyan has accused Turkey of "trying to divert world attention" from the Yerevan commemorations.