The United States irked its key ally Turkey on Monday, criticizing 1915 massacres in Armenia as "one of the worst mass atrocities of the 20th century," although stopping short of calling them genocide.
The issue is a politically fraught one in the United States especially among Armenian Americans.
Estimates say the killings number between half a million and 1.5 million.
The largest group is in the Los Angeles area, and includes pop star and actress Cher, and the Kardashians of reality television fame.
Former president Barack Obama had promised to recognize the killings as a genocide. But over eight years in office, in need of cooperation from Turkey, he did not follow through.
New President Donald Trump issued a statement saying bluntly that "today, we remember and honor the memory of those who suffered during the Meds Yeghern, one of the worst mass atrocities of the 20th century."
Many of the diaspora landed in countries from France to Argentina to the United States.
"Beginning in 1915, one and a half million Armenians were deported, massacred, or marched to their deaths in the final years of the Ottoman Empire," Trump said.
"I join the Armenian community in America and around the world in mourning the loss of innocent lives and the suffering endured by so many.
"We must remember atrocities to prevent them from occurring again," he continued.
"We welcome the efforts of Turks and Armenians to acknowledge and reckon with painful history, which is a critical step toward building a foundation for a more just and tolerant future."
Amid sharp Turkish criticism for the remarks, the State Department noted that the US president, in fact, had made no mention of genocide.
"The (Trump) statement that was put out is consistent with the statements that have been put out for at least several of the past administrations," White House spokesman Sean Spicer told a briefing.
"I think if you look back to the language that President Obama, President Bush have used, the language the President used is consistent with all of that," Spicer stressed.
In Istanbul, the foreign ministry said Trump's remarks on the remembrance day were "misinformation" and "false definitions."
"We expect from the new US administration not to accredit the one-sided historical narrative of these circles which are known for their tendency to violence and hate speech and to adopt an approach which will take into consideration the sufferings of all sides," it stressed.
Outside the Turkish embassy here, a few hundred protested on each side, separated by the road and police.
House Democrat Steny Hoyer of Maryland said that "on this day in 1915, the arrest of Armenian social, political, and intellectual leaders launched a four-year campaign of genocide that took the lives of 1.5 million men, women, and children.
"Not only must we recommit ourselves to the remembrance of the twentieth century's first genocide but also work to prevent ethnic killing in the twenty-first century," he argued.