President Biden recognized the massacre of Armenians by the Ottoman Empire as a genocide Saturday, a designation that U.S. presidents long avoided for fear of damaging the U.S.-Turkey relationship.

The decision follows a lengthy lobbying campaign by members of Congress and Armenian American groups eager to see the White House use a term embraced by many scholars of early 20th century history.

“The American people honor all those Armenians who perished in the genocide that began 106 years ago today,” Biden said in a statement. “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.”

Historians estimate that 1.5 million Armenians were killed in a campaign of forced marches and mass killings born out of Ottoman concerns that the Christian Armenian population would align with Russia during World War I, abetting an archnemesis of the Ottoman Turks.

Turkey has acknowledged that many Armenians were killed in fighting with Ottoman forces beginning in 1915 but disputes the larger casualty counts, denies that the events constituted genocide and considers such claims a slander against its founder, Mustafa Kemal Ataturk.

Turkey’s foreign minister, Mevlut Cavusoglu, immediately criticized Biden’s remarks.

“We entirely reject this statement,” he wrote on Twitter. “We have nothing to learn from anybody on our own past. Political opportunism is the greatest betrayal to peace and justice.”

The move comes amid worsening relations between the United States and Turkish President Recep Tayyip Erdogan over Turkey’s purchases of Russian military equipment, human rights abuses and interventions in Syria and Libya.

Biden called Erdogan on Friday, but a White House readout of the conversation did not mention the 1915 massacres. Biden conveyed his interest in a “constructive bilateral relationship with expanded areas of cooperation and effective management of disagreements,” the statement said.

The Turkish readout of the call said Erdogan raised his objections about U.S. support for Kurdish forces in Syria, whom Turkey considers terrorists, and the case of Fethullah Gulen, a religious leader who lives in exile in the United States.

Biden’s recognition came on April 24, the date Ottomans seized Armenian leaders and intellectuals in Istanbul in 1915 in what many scholars view as the opening phase of the first genocide of the 20th century.

In his statement honoring the victims of the massacre, Biden praised the contributions of the Armenian diaspora, including in the United States.

“With strength and resilience, the Armenian people survived and rebuilt their community,” Biden said. “Over the decades Armenian immigrants have enriched the United States in countless ways, but they have never forgotten the tragic history that brought so many of their ancestors to our shores.”

Armenian American groups hailed the long-sought move on Saturday.

“President Biden’s affirmation of the Armenian Genocide marks a critically important moment in the arc of history in defense of human rights,” said Bryan Ardouny, executive director of the Armenian Assembly of America. “By standing firmly against a century of denial, President Biden has charted a new course.”

President Ronald Reagan referred to the massacre as a genocide early in his first term, but his successors had not out of concern for alienating Turkey, a NATO ally that was for years considered a strategically valuable member of the military alliance.

Several U.S. presidents, even those who had promised on the campaign trail to issue a declaration, remained mindful of this sensitivity and instead called the killings a “massacre” or “horrific tragedy.”

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

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 Soner Cagaptay, a Turkey scholar at the Washington Institute, who also noted strong disagreement over Turkey’s actions in Iraq and Syria. “Now the opposite is true.”

Lawmakers in Congress, including those with large Armenian American constituencies, hailed the decision.

“I commend President Biden’s decision to formally recognize the Armenian Genocide,” said Sen. Elizabeth Warren (D-Mass.). “Calling this atrocity what it was — genocide — is long overdue. We must recognize the horrors of the past if we hope to avoid repeating them in the future.”

In Armenia’s capital, Yerevan, people laid flowers and gathered at a hilltop memorial with an eternal flame to the victims of the massacres and deportations by the Ottomans.

Armenia’s deputy foreign minister, Avet Adonts, said at the memorial Saturday that Biden’s declaration was an “important step.”

“It will also serve as an example for the rest of the civilized world,” he said, the Associated Press reported.

In Turkey, the Foreign Ministry posted videos and messages commemorating the deaths of Turkish diplomats who were killed in decades past by Armenian militants. Erdogan sent a message to Bishop Sahak Mashalian, the head of the Armenian Patriarchate in Istanbul, evoking what he said was the “centuries-old culture” of coexistence between Turks and Armenians and warning against “politicization” of the relationship by “third parties,” according to the state-run Anadolu news agency.

A coronavirus lockdown in Istanbul prevented gatherings to commemorate the mass killings, including what has become an annual pilgrimage to the gravesite of Sevag Balikci, a Turkish Armenian soldier who was killed on April 24, 2011, in what the authorities initially called an accidental shooting and what Armenian activists said was a hate crime.

The annual gatherings have also included another Istanbul landmark: the Museum of Turkish and Islamic Arts, which more than a century ago was the Ottoman police station where hundreds of Armenian intellectuals were held after being rounded up in the city on April 24, 1915.

While Turkish authorities have permitted some of the commemorations, in recent years they have prevented other gatherings, as part of a wider crackdown by the government on protests or expressions of dissent.

Garo Paylan, a Turkish parliament member who is Armenian, said: “I am not happy with Biden’s decision, and I am not sad. I feel sorry because of the denial which has been going for 106 years. My pain is the subject of other parliaments, of other leaders.” His political party, the Peoples’ Democratic Party, or HDP, was the only major Turkish political party to acknowledge the genocide in a statement Saturday, drawing angry rebukes from Turkish government officials.

“I believe the only country where Armenians can find justice is Turkey,” he added. “And Turkey is far away from justice. Mr. Biden’s decision is not going to heal our wound.”

In a lengthy statement, Turkey’s Foreign Ministry asserted that Biden’s decision was made “under pressure of radical Armenian circles and anti-Turkey groups.” With regards to the events of 1915, it added, “none of the conditions required for the use of the term ‘genocide’ that is strictly defined in international law are met.”

“This statement of the US, which distorts the historical facts, will never be accepted in the conscience of the Turkish people, and will open a deep wound that undermines our mutual trust and friendship,” it said.

Fahim reported from Istanbul.