President Biden is expected to recognize the mass killing of Armenians by the Ottoman Empire during World War I as a genocide, according to two people familiar with the decision, breaking a decades-long tradition of U.S. presidents refraining from using the term for fear of jeopardizing U.S.-Turkish relations.

The anticipated move would fulfill a campaign promise Biden made in October and reflect his willingness to anger Turkish President Recep Tayyip Erdogan amid a growing list of disagreements over Turkey’s arms deals with Russia, democratic backsliding, and interventions in Syria and Libya.

It would also be the second time the Biden administration has formally declared a genocide at the risk of infuriating a major power, following its determination that China is carrying out a genocide against Uyghur Muslims in the Xinjiang region.

Historians estimate that 1.5 million Armenians were killed in the brutal campaign and commonly classify the killings as a genocide. Biden’s acknowledgment would represent a major victory for the Armenian American diaspora, which has lobbied for recognition for years.

“I am proud the U.S. government is poised to finally be able to say it without any euphemism: genocide is genocide. Plain and simple,” said a statement by Sen. Robert Menendez (D-N.J.), the chairman of the Senate Foreign Relations Committee, whose wife is of Armenian ancestry.

If Biden moves forward, the reaction from Turkey is likely to be swift.

On Tuesday, Turkish Foreign Minister Mevlut Cavusoglu said the designation would damage the bilateral relationship and represent an affront to “international law.”

“Statements that have no legal binding will have no benefit, but they will harm ties,” Cavusoglu said. “If the United States wants to worsen ties, the decision is theirs.”

Turkey has acknowledged that many Armenians were killed in fighting with Ottoman forces in 1915 but disputes the larger casualty counts and denies that the events constituted genocide.

The designation would be in line with an effort that Biden’s top diplomat, Antony Blinken, has called “putting human rights at the center of U.S. foreign policy,” a standard he has been challenged on regarding the U.S. approach to Saudi Arabia, Egypt and other autocratic regimes.

The people familiar with the decision spoke on the condition of anonymity to discuss the president’s future moves.

White House press secretary Jen Psaki declined to comment on the pending decision Wednesday but said the administration would have “more to say” on the topic on Saturday.

That day, April 24, is the date Ottomans apprehended Armenian dignitaries in Istanbul in 1915 in what many scholars view as the opening phase of the first genocide of the 20th century. The campaign of forced marches and mass killings was born out of Ottoman concerns that the Christian Armenian population would align with Russia, an arch nemesis of the Ottoman Turks.

In anticipation of the decision, Armenian American groups have begun hailing the move as a milestone in defending human rights.

“Affirmation of the Armenian Genocide enhances America’s credibility and recommits the United States to the worldwide cause of genocide prevention,” Bryan Ardouny, executive director of the Armenian Assembly of America, said in a statement.

“For many Armenian Americans, a trauma denied is a trauma unresolved, so the statement is psychologically important,” said Thomas de Waal, a Caucasus scholar and author of the book “Great Catastrophe: Armenians and Turks in the Shadow of Genocide.” “Some of their grandparents ended up in unmarked graves in Syria or Eastern Turkey. They have felt that the suffering and losses that their families endured weren’t given the prominence they deserve.”

President Ronald Reagan referred to the killings as genocide during his time in office, but none of his successors have for fear of alienating Turkey, a NATO ally that views the term as slander against its founder, Mustafa Kemal Ataturk.

Several past U.S. presidents, even those who promised to recognize the Armenian genocide on the campaign trail, remained mindful of this sensitivity and instead called the incident a “massacre” or “horrific tragedy.”

Besides Biden’s avowed commitment to human rights, analysts say the president has had a freer hand than other U.S. presidents because of the continued drift in the U.S.-Turkish relationship under Erdogan’s leadership.

“Unlike previous presidents who were briefed by bureaucrats on why Turkey is such an important ally and why this is the wrong time to do it, Biden had none of this served to him this time,” said Soner Cagaptay, a Turkey scholar at the Washington Institute.

In past years, the Defense Department and the State Department’s Bureau of European and Eurasian Affairs would advise presidents against labeling the atrocity a genocide. But U.S. officials, particularly at the Pentagon, have been furious with Erdogan over his purchase of the Russian S-400 missile defense system, which they say is incompatible with NATO’s military equipment and a threat to the alliance’s security.

“The Defense Department was Turkey’s biggest fan,” said Cagaptay, who also noted strong disagreement over Turkey’s actions in Iraq and Syria. “Now, the opposite is true.”

Turkey’s government communications office briefly addressed the issue in a statement released Thursday, quoting Erdogan during a meeting with his presidential advisory board in Ankara as saying that Turkey would “continue to defend the truth against the so-called ‘Armenian genocide’ lie and those who support this slander with political calculations.”

Kareem Fahim in Istanbul contributed to this report.