Joe Biden has become the first president of the US to call the 1915 massacre of Armenians genocide formally.
The killings took place in the waning days of the forerunner of modern-day Turkey, the Otterman Empire.
The issue is susceptible with Turkey accepting the slaughter but is denying the term genocide.
On Saturday, foreign minister Mevlut Cavusoglu said that Turkey is wholly rejecting the US verdict.
He tweeted that they will not take any lessons on their history.
Later the Turkish foreign ministry said it had asked the US Ambassador to convey Ankara’s strong reaction.
Before this, none of the US administrations has ever used the word genocide formally in a statement. In concerns that it might damage the relations with Turkey, a Nato ally.
Ottoman Turks have accused Christian Americans of treachery after suffering a defeat at the hands of Russian forces. Then they began deporting them en masse to the Syrian desert and elsewhere.
Hence, hundreds and thousands of Armenians were massacred or died of starvation and disease.
Atrocities were widely noted at the time by witnesses, including journalists, diplomats, and missionaries.
The number of Armenian deceased has always been debated. Armenians say about 1.5 million people died, while Turkey figures it to be around 3,00,000. Additionally, according to the International Association of Genocides Scholars (IAGS), the death toll was over a million.
Turkish officials have affirmed that the atrocities took place. However, they contend that there was no systematic effort to destroy the Christian Armenian people. Turkey tells many Muslim Turks in the riot of World War One died as well.
A further statement from Joe Biden
Mr Biden’s statement, released as Armenia remembers the start of the mass slaughter. He said they retain the lives of all those who fell in the Ottoman-era genocide. So they recommit themselves in stopping such atrocities from befalling ever again.
Also, that they retain so that they remain ever-alert on the eroding impact of hate in all its forms.
Mr Biden said the purpose was not to cast blame but to assure that what followed is never repeated.
He had previously welcomed a move by the US House of Representatives of 2019. In it voted strongly to identify the mass massacre as genocide.