Joe Biden has formally recognised the killing of an estimated 1.5 million Armenians by the Ottoman Empire in the early 20th century as genocide.
The US president used the term after decades of his predecessors avoiding it for fear of alienating Turkey.
Recognising the killings – which occurred between 1915 and 1923 – was a campaign promise for the 78-year-old.
Turkey in 1915, when Armenians were marched long distances towards the Syrian desert. Pic: Associated Press
It is not known exactly how many people died as Armenians were marched from their homes in what is now Turkey towards the Syrian desert by the Ottoman Empire.
An estimated two million Armenians were deported in the events, which Armenians refer to as Meds Yeghern, or the Great Crime.
Using a presidential proclamation, Mr Biden said: “Each year on this day, we remember the lives of all those who died in the Ottoman-era Armenian genocide and recommit ourselves to preventing such an atrocity from ever again occurring.
“Beginning on 24 April 1915, with the arrest of Armenian intellectuals and community leaders in Constantinople by Ottoman authorities, one and a half million Armenians were deported, massacred, or marched to their deaths in a campaign of extermination.
“We honour the victims of the Meds Yeghern so that the horrors of what happened are never lost to history.
“And we remember so that we remain ever-vigilant against the corrosive influence of hate in all its forms.”
Members of the Armenian diaspora gather in Montebello, California
Mr Biden reportedly informed Turkey’s President Recep Tayyip Erdogan that he was going to make the announcement in a call on Friday.
While neither country mentioned this in their readouts from the conversation, the statement from the White House did say that the US leader told his Turkish counterpart that he wanted to improve the relationship between the country and find “effective management of disagreements”.
The pair will also hold a bilateral meeting at the NATO summit in Brussels in June.
Turkey’s President Tayyip Erdogan
In the Armenian capital of Yerevan on Saturday, people climbed to a hilltop complex to memorialise victims with flowers – creating a wall of blooms 7ft high.
Armenian deputy foreign minister Avet Adonts, speaking at the memorial before Mr Biden issued his proclamation, said a US president using the term genocide would “serve as an example for the rest of the civilised world”.
A Lebanese-Armenian bishop adjusts his garment inside the cemetery of Armenians. Pic: Associated Press
Mr Biden’s statement added: “Today, as we mourn what was lost, let us also turn our eyes to the future – toward the world that we wish to build for our children.
“A world unstained by the daily evils of bigotry and intolerance, where human rights are respected, and where all people are able to pursue their lives in dignity and security.”
People lay flowers at the eternal fire of the Tsitsernakaberd memorial in Yerevan
“Let us renew our shared resolve to prevent future atrocities from occurring anywhere in the world. And let us pursue healing and reconciliation for all the people of the world,” he continued.
“The American people honour all those Armenians who perished in the genocide that began 106 years ago today.”