President Donald Trump is recalling the death and suffering of more than 1 million Armenians during the final years of the Ottoman Empire, without describing it as genocide.
Such a declaration would anger Turkey, whose cooperation Trump seeks in Syria.
Trump says in a statement that the World War I-era killing of Armenians represents one of the 20th century's worst mass atrocities, and a "dark chapter" in history.
He adds that remembering will "prevent them from occurring again."
The issue also confronted Trump's predecessor, Barack Obama, and other presidents.
Obama promised as a candidate to describe the killing as genocide, if elected. But he repeatedly stopped short of doing so once in office.
Samantha Power, Obama's U.N. ambassador, however, did describe it as genocide during a speech in late 2016.