US President Donald Trump (R) and Turkish President Recep Tayyip Erdogan attend a joint press conference at the White House in Washington D.C. on Nov. 13, 2019. Donald Trump and Recep Tayyip Erdogan failed to reach agreement on major bilateral differences during their Wednesday's meeting at the White House. (Photo by Ting Shen/Xinhua)

The US Senate on Thursday unanimously passed a resolution that recognizes as a genocide the mass killings of Armenians a century ago, a historic move that infuriated Turkey and dealt a blow to the already problematic ties between Ankara and Washington.

Turkey condemned the measure, which passed a month after an official visit to the White House by Turkish President Tayyip Erdogan, who enjoys a special rapport with President Donald Trump, amid mounting issues that have soured the relationship between the two NATO allies.

The Democratic-led House of Representatives had passed the resolution by an overwhelming majority in October. But a vote in the Senate was repeatedly blocked by Trump's fellow Republican senators since meeting with Erdogan.

"This is a tribute to the memory of 1.5 million victims of the first #Genocide of the 20th century and bold step in promotion of the prevention agenda. #NeverAgain," Armenian Prime Minister Nikol Pashinyan tweeted in English.

The resolution asserts that it is US policy to commemorate as genocide the killing of 1.5 million Armenians by the Ottoman Empire. The Ottoman Empire was centered in present-day Turkey.