WASHINGTON (Reuters) - Republican Senator Kevin Cramer prevented the U.S. Senate from voting on a resolution on Thursday that would recognize as a genocide the mass killings of Armenians a century ago, saying it was not an appropriate time to pass legislation that would anger Turkey.

The Democratic-led House of Representatives passed the resolution by an overwhelming 405-11 in late October. But there has not been a vote in the Senate, where President Donald Trump’s fellow Republicans hold a majority of seats.

Congressional aides said the White House does not want the legislation to move ahead while it negotiates with Ankara on sensitive issues such as Turkey’s offensive against Kurdish fighters in northern Syria and the NATO ally’s purchase of an S-400 missile defense system from Russia, which could provoke U.S. sanctions.

The resolution asserts that it is U.S. policy to commemorate as genocide the killing of 1.5 million Armenians by the Ottoman Empire from 1915 to 1923. The Ottomon Empire was centered in present-day Turkey.

Turkey accepts that many Armenians living in the Ottoman Empire were killed in clashes with Ottoman forces during World War One, but contests the figures and denies that the killings were systematically orchestrated and constitute a genocide.

Ankara views foreign involvement in the issue as a threat to its sovereignty. It immediately denounced the House vote.

Democratic Senator Bob Menendez and Republican Senator Ted Cruz tried to force a Senate vote on the resolution on Thursday. Cramer blocked it, saying the time was not right just after Trump held talks with Turkish President Tayyip Erdogan at NATO summit in London.

“I don’t think there’s a single member of the Senate who doesn’t have serious concerns about Turkey’s behavior,” Cramer said, adding, “At the right time, we may pass it.”

Menendez disagreed, noting Erdogan recently visited Washington and nothing had changed. He promised to come to the Senate chamber once a week to raise the issue.

“I am not going to cease until we do what is morally and principally right,” Menendez said.

For decades, measures recognizing the Armenian genocide have stalled in the U.S. Congress, stymied by concerns about relations with Turkey and intense lobbying by the Ankara government.

The House vote marked the first time in 35 years such legislation was considered in the full chamber, underscoring widespread frustration in Congress with the Turkish government, from members of both U.S. political parties.