A Republican United States Senate member on Thursday blocked a resolution recognising the "Armenian genocide", the second time in a week that a member of President Donald Trump's party halted the measure.
Senator David Perdue prevented a bipartisan effort to pass the resolution by unanimous consent, arguing that its passage during a sensitive period "would undermine the administration's commitment to overcoming real challenges in our bilateral relationship with Turkey".
The move angered Senate Democrat Robert Menendez, whose effort had been rebuffed the previous week after Republican congressmen met with visiting Turkish President Recep Tayyip Erdogan.
"It is amazing to me that the greatest superpower on the face of the earth just can't speak [the] truth of history," Menendez said.
Menendez noted that he has pressed for recognition of the atrocity for more than 10 years, and will force more votes on the issue. "I'm not going to relent," he said.
Armenians say up to 1.5 million of their kin were killed between 1915 and 1917 as the Ottoman Empire was falling apart.
They say the mass killings amounted to "genocide", a claim recognised by some 30 countries.
Turkey strongly denies the accusation of "genocide" and says Armenians and Turks died as a result of World War I. It puts the death toll in the hundreds of thousands from both sides.
Joining Menendez in his resolution effort was Republican Senator Ted Cruz, who described "the Ottoman Empire's calculated extermination of the Armenians" that "no amount of political double-speak can cover up".
Last month the House of Representatives overwhelmingly approved a similar resolution officially recognising the "Armenian genocide", infuriating Turkey.
Turkey has slammed the House of Representatives' resolution, warning it risks harming ties "at an extremely fragile time" for international and regional security.
"The resolution which has apparently been drafted and issued for domestic consumption is devoid of any historical or legal basis," Turkey's foreign ministry said in a statement last month.
The measure was passed alongside a bill that sought to impose sanctions over Ankara's assault on Kurdish-controlled territory in northeast Syria, which was made possible by the withdrawal of American troops. The US Senate has not passed the latter either.
In 2017, newly-inaugurated President Trump criticised the killings as "one of the worst mass atrocities of the 20th century", but in keeping with long-standing US practice, he stopped short of using the word "genocide".
Before being elected in 2008, Trump's predecessor Barack Obama had pledged to recognise the "genocide" but ultimately did not do so during his two terms in office.