President Biden on Saturday recognized the mass killings of Armenians more than a century ago as genocide, signaling a willingness to test an increasingly frayed relationship with Turkey, long a key regional ally and an important partner within NATO.

“Each year on this day, we remember the lives of all those who died in the Ottoman-era Armenian genocide and recommit ourselves to preventing such an atrocity from ever again occurring,” Mr. Biden said in a statement issued on the 106th anniversary of the beginning of a brutal campaign by the former Ottoman Empire that killed 1.5 million people. “And we remember so that we remain ever vigilant against the corrosive influence of hate in all its forms.”

The declaration by Mr. Biden reflected his administration’s commitment to human rights, a pillar of its foreign policy. It is also a break from Mr. Biden’s predecessors, who were reluctant to anger a country of strategic importance and were wary of driving its leadership toward American adversaries like Russia or Iran.

The Turkish government, as well as human rights activists and ethnic Armenians, gave a muted response to the news, which leaked days in advance, describing the move as largely symbolic. Later on Saturday, the country’s foreign minister summoned the U.S. ambassador to protest the declaration, state media reported.

President Recep Tayyip Erdogan, who has repeatedly denied that the killings amounted to genocide, had lobbied hard to prevent the announcement, mounting a conference and media campaigns before the anniversary on Saturday.

But in a call on Friday, Mr. Biden told Mr. Erdogan directly that he would be declaring the massacre an act of genocide, according to a person familiar with the discussion who spoke on the condition of anonymity to disclose details of the conversation.