(Bloomberg) -- President Joe Biden is poised to became the first U.S. president in 40 years to recognize the 1915 mass killings of Armenians as genocide, according to a person familiar with the matter, a move that risks upsetting an already tenuous relationship with Turkey, a NATO ally.

Biden’s pronouncement, the person said on condition of anonymity, will likely coincide with Saturday’s Armenian Genocide Remembrance Day. The declaration would make good on a promise by Biden in his successful campaign for office.

Such a declaration will almost certainly prompt a swift backlash from Turkey, the successor state to the Ottoman Empire, under which the genocide was carried out. Turkish Foreign Minister Mevlut Cavusoglu told the news site Haberturk this week that Biden’s words had no legal effect and would only harm the U.S.-Turkey relationship. “If the United States wants to worsen ties, the decision is theirs,” he said.

Turkey’s president, Recep Tayyip Erdogan, has lashed out at other countries that have declared the executions and organized massacres of 1915 a genocide.

By breaking with predecessors who used more moderate language, Biden would deploy that label, which many Armenian-Americans have long waited to hear.

Turkish-American relations have already been strained over Turkey’s decision to purchase an air defense system from Russia, which led the Trump administration to impose unprecedented sanctions against a member of NATO.

During last year’s presidential campaign, Biden promised to “recognize the Armenian Genocide and make universal human rights a top priority.”

Still, the actual language of the declaration was not a foregone conclusion. President Barack Obama had made a similar promise in 2008. But in eight years in office, he issued only watered-down statements calling the events of 1915 “a tragedy” a “mass atrocity” and a “horror” — but not a genocide.

President Ronald Reagan was the last American leader to refer to a genocide in a 1981 proclamation, but backtracked under pressure from Turkey.

Under international law, genocide refers to the killing, injuring or forcible removal of people with “intent to destroy, in whole or in part, a national, ethnic, racial or religious group.”

Turkey maintains that the Ottoman regime merely intended to resettle Armenians and not kill them — a claim largely rejected by modern historians.

In 2019, both houses of Congress adopted a resolution recognizing the genocide. That vote occurred as the dispute over the anti-aircraft missiles continued and after Turkey began a military campaign in northern Syria. That operation started after President Donald Trump abruptly withdrew troops from the Kurdish-held region.

Earlier that year, Erdogan said in a Twitter post, saying that “The relocation of the Armenian gangs and their supporters, who massacred the Muslim people, including women and children, in eastern Anatolia, was the most reasonable action that could be taken in such a period.”

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