US President Joe Biden on Saturday said the 1915 massacres of Armenians in the Ottoman Empire constituted genocide, a historic declaration that infuriated Turkey and is set to further strain already frayed ties between the two NATO allies.

The largely symbolic move, breaking away from decades of carefully calibrated language from the White House, will likely be celebrated by the Armenian diaspora in the United States, but comes at a time when Ankara and Washington have deep policy disagreements over a host of issues.

Turkish Foreign Minister Mevlut Cavusoglu said Turkey “entirely rejects” the US decision which he said was based “solely on populism.”

“We have nothing to learn from anybody on our own past. Political opportunism is the greatest betrayal to peace and justice,” Cavusoglu said on Twitter.

In his statement, Biden said the American people honour “all those Armenians who perished in the genocide that began 106 years ago today.”

“Over the decades Armenian immigrants have enriched the United States in countless ways, but they have never forgotten the tragic history … We honor their story. We see that pain. We affirm the history. We do this not to cast blame but to ensure that what happened is never repeated,” Biden said.

In comments that sought to soften the blow, a senior administration official told reporters that Washington encouraged Armenia and Turkey to pursue reconciliation and continues to view Ankara as a critical NATO ally.

For decades, measures recognizing the Armenian genocide stalled in the US Congress and US presidents have refrained from calling it that, stymied by concerns about relations with Turkey and intense lobbying by Ankara.

Turkey accepts that many Armenians living in the Ottoman Empire were killed in clashes with Ottoman forces during World War One, but contests the figures and denies the killings were systematically orchestrated and constitute a genocide.

Ties between Ankara and Washington have been strained over issues ranging from Turkey’s purchase of Russian S-400 defense systems – over which it was the target of US sanctions – to policy differences in Syria, human rights and legal matters.

Biden’s declaration follows a non-binding resolution by the US Senate adopted unanimously in 2019 recognizing the killings as genocide.