Six Republican senators are calling on Secretary of State Rex Tillerson to explain reports that top State Department lawyers are systematically removing the word "genocide" to describe the Islamic State's slaughter of Christians, Yazidis, and other ethnic minorities in Iraq and Syria from official agency documents.

Sens. Marco Rubio (R., Fla.), Majority Whip John Cornyn, (R., Texas), Roy Blunt, (R., Mo.,), Cory Gardner, (R., Colo.), James Lankford (R., Okla.), and Ben Sasse, (R., Neb.) sent a letter to Tillerson Thursday requesting "urgent clarification" on the administration's policy on recognizing ISIS mass slaughter of Christians, Yazidis, and other minorities in Iraq as "genocide."

The senators noted that both President Donald Trump and Vice President Mike Pence have denounced "this ‘genocide'" in public statements in recent months.

The Washington Free Beacon on Tuesday first reported that Obama "holdover" attorneys at the State Department were removing references to "genocide" against Christians and other religious minorities in Iraq, according to human rights activists and attorneys familiar with the policies.

"We write regarding disturbing reports that the State Department's Office of Legal Adviser has sought to undermine and perhaps roll back the determination of your predecessor, Secretary of State John Kerry, that ISIS is ‘responsible for genocide' against Christians, Yezidis, and other religious minorities," they said in their letter.

"Next week marks three years since the Islamic State waged a brutal offensive in Iraq, laying siege to Mt. Sinjar, overtaking Iraq's largest Christian city, Qaraqosh, and murdering, enslaving, displacing, and otherwise terrorizing thousands of religious minorities, whose community's roots in these lands go back to antiquity," they wrote. "The full measure of human suffering exacted against these innocents is incalculable."

The senators asked whether Tillerson authorized or supported the deletion of the word "genocide" at is relates to Christians, Yazidis, and other minorities in Iraq from official documents, how widespread the practice is, and whether State Department attorneys issued any guidance or directives in recent months about the use of the word "genocide" in reference to these populations.

"As we approach this solemn anniversary, and with it persistent questions regarding the long-term viability of these ancient communities, it is vital that we have clarity regarding the policy of this administration, specifically as it relates to the most egregious of all human rights atrocities, genocide," they wrote.

"As such, we respectfully request urgent clarification on this matter including answers to the following questions:

Has the Legal Adviser issued any guidance or directives in recent months that would contradict or undermine Secretary Kerry's determination? If so, please provide the language.

If the Legal Adviser has engaged on this issue, have you supported these efforts?"

A State Department spokesman Thursday told the Free Beacon that "we are not going to comment on internal processes."

"However, we can say that the premise of a recent article on this issue is inaccurate. We have not removed the word genocide from documents," the spokesman said. "Furthermore, I can confirm that it is the secretary of state's judgement that ISIS is responsible for genocide against groups in areas it controlled, including Yazidis, Christians, and Shia Muslims."

The spokesman declined to answer a series of follow-up questions, including whether the word "genocide" was removed in any speech written for Tillerson, whether the Office of Legal Adviser ever advised officials to remove the word genocide from any document, finalized or still in the writing process, since President Trump took office, and whether top State Department officials declined to recognize the anniversary of Kerry's March 2016 genocide determination despite an effort by some officials to commemorate it.

"Again, we are not going to comment on internal processes," the spokesman said in response.

State Department press secretary Heather Nauert told reporters Thursday that it is "categorically false" that officials removed references to genocide against Christians and Yazidis from documents.

"We have looked through documents ourselves—the word genocide is in there—that has not been removed," she said.

She said that Tillerson "firmly believes" that Christians and Yazidis were victims of ISIS genocide but declined to take any follow up questions.

"Okay, that's all I'm going to say about that. I hope I've been clear," she said.

Human rights activists and Catholic leaders are worried that recent efforts at the State Department to avoid using the word "genocide" in reference to religious minorities in Iraq is aimed at rolling back Kerry's decision. Kerry's much-anticipated genocide designation came after months of equivocation and detailed documentation by interested parties that the Islamic State is responsible for genocide against Yazidis, Christians, and Shia Muslims.

The senators expressed similar concerns, stressing that Kerry only made the genocide determination after Congress forced Kerry to come to a conclusion on the genocide question. Congress passed language in the 2016 omnibus spending bill requiring the State department to weigh the detailed evidence and make a conclusion.

Kerry announced his decision at a March 2016 press conference called for that purpose, the senators said.

"It was only the second time in history that a U.S. secretary of state made a genocide determination and it was widely heralded," they wrote. "Both the U.S. Senate and House of Representatives unanimously passed resolutions along similar lines."

Rubio, along with a bipartisan group of Capitol Hill lawmakers and activists, was hoping that the genocide designation would help direct millions of dollars in relief funds to Christian, Yazidi, and other persecuted religious minority communities in Iraq.

ISIS murders and kidnappings have decimated the Christian population in Iraq, which numbered between 800,000 and 1.2 million in 2002, reducing it to fewer than 250,000 now. Without action, activists and charities say, Christians could disappear completely from Iraq in the near future.

After meeting with Pope Francis in May, President Trump vowed to do everything in his power to defend and protect the "historic Christian communities of the Middle East."

Activists and Catholic leaders are now calling on Trump to turn the rhetoric into action on the ground and help get U.S. aid to these persecuted communities trying to rebuild their homes and their lives in Iraq.