President Barack Obama on Wednesday called the mass killings of Armenians at the hands of the Ottoman Turks in 1915 "one of the worst atrocities of the 20th century," but again broke a 2008 campaign promise to label the tragedy a "genocide." Doing so would have angered NATO ally Turkey.

"Ninety-eight years ago, 1.5 million Armenians were massacred or marched to their deaths in the final days of the Ottoman Empire. We pause to reflect on the lives extinguished and remember the unspeakable suffering that occurred," Obama said in a statement released by the White House. "In so doing, we are joined by millions across the world and in the United States, where it is solemnly commemorated by our states, institutions, communities, and families. We also remind ourselves of our commitment to ensure that such dark chapters of history are not repeated."

Obama, who called the massacre "genocide" during his 2008 run for the White House and vowed to use the term as president, stopped short of doing so in his statement, as he has in the past. Turkey, a NATO member, fiercely disputes the genocide charge and has warned that formal U.S. steps to use the term will hamper relations. Turkey's ambassador to Washington, Namik Tan, sharply criticized a similar statement from Obama in 2011, taking to Twitter to denounce it as inaccurate, flawed and one-sided.

"Nations grow stronger by acknowledging and reckoning with painful elements of the past, thereby building a foundation for a more just and tolerant future," Obama said in an implicit appeal to Turkey. "We appreciate this lesson in the United States, as we strive to reconcile some of the darkest moments in our own history. We recognize those courageous Armenians and Turks who have already taken this path, and encourage more to do so, with the backing of their governments, and mine."

The chairman of the Armenian National Committee of America, Aram Hamparian, denounced Obama’s statement, accusing the president of bowing to Turkey’s “gag rule” on the issue.

Story continues

"Our President's complicity in Turkey's denial of truth and its ongoing obstruction of justice will not derail our progress toward a truthful, fair, and comprehensive international resolution of Turkey's still unpunished crime against the Armenian nation,” Hamparian said in a statement.

Armenian-American celebrity Kim Kardashian marked the event on her official Twitter feed, @kimkardashian.

Please help me get this trending today! It means a lot to me!#RecognizeArmenianGenocide Everyone RT — Kim Kardashian (@KimKardashian) April 24, 2013

The issue is a powerful one for Armenian-Americans. The Armenian Reporter news site has repeatedly and forcefully condemned what it mockingly calls "amnesia" on the part of Obama and former Secretary of State Hillary Clinton, who as senators co-sponsored a resolution calling for the use of the term "genocide" when discussing the tragedy.

On Oct. 2, 2008, the paper published a letter from then-candidate Obama in which he trumpeted "my firmly held conviction that the Armenian Genocide is not an allegation, a personal opinion, or a point of view, but rather a widely documented fact supported by an overwhelming body of historical evidence."

"The facts are undeniable. An official policy that calls on diplomats to distort the historical facts is an untenable policy," Obama wrote. "As President I will recognize the Armenian Genocide."

Twenty-two countries have recognized the events of 1915 as genocide, and 42 U.S. states have done so as well, either by legislation or proclamation. Congressional resolutions aimed at doing the same at the national level have never become law. Successive presidents have objected on grounds that doing so risks angering Turkey.