U.S. spy agencies are preparing to deliver a classified briefing to Republican presidential nominee Donald Trump, the nation’s intelligence director said Thursday, despite deep unease among many spy officials with the real estate mogul’s pro-Russian rhetoric.

National Intelligence Director James R. Clapper Jr. indicated that Trump and Democratic nominee Hillary Clinton are eligible to receive intelligence briefings within days of the conclusion of the Democratic National Convention.

“Now is the appropriate time, since both candidates have been officially anointed,” Clapper said during public remarks at a security conference here.

Amid reports that some intelligence officials have deep reservations about sharing sensitive information with Trump, Clapper said that “it is not up to the administration and not up to me personally to decide on the suitability of presidential candidates. The American electorate is deciding on the suitability of the next commander in chief.”

But Clapper’s remarks came amid new signs of deep discomfort with Trump among the upper ranks of the intelligence community. In a measure of that growing animosity, one senior intelligence official said Wednesday that he would decline to participate in any session with Trump.

Retired Navy admiral and law professor John Hutson used his speech at the Democratic convention to question Donald Trump's ability to keep America safe. (The Washington Post)

“I would refuse,” the official said, citing not only concern with Trump’s expressions of admiration for Russian President Vladi­mir Putin but seeming uninterest in acquiring a deeper or more nuanced understanding of world events.

“He’s been so uninterested in the truth and so reckless with it when he sees it,” the official said. He and others spoke on the condition of anonymity, citing a desire to speak candidly about domestic political issues that intelligence officials typically refuse to discuss.

Clapper’s comments seemed aimed at quelling a rising chorus of such voices among analysts and other officials at U.S. spy agencies who have expressed dismay with Trump’s positions on a range of issues, including his vow earlier this year to order the CIA to resume using brutal interrogation methods that were banned and widely condemned as torture.

Trump’s quip this week goading Russia’s intelligence services — widely suspected of hacking the Democratic National Committee’s email servers — to target Clinton’s accounts while serving as secretary of state was seen as particularly incendiary among intelligence professions who regard Russia as a bitter foe.

Trump triggered the controversy Wednesday when he said, “Russia, if you’re listening, I hope you’re able to find the 30,000 emails that are missing” from a broader collection that Clinton turned over to the FBI and the State Department. Clinton has said she deleted nearly 32,000 emails from her time as secretary because they were personal and dealt with subjects such as her daughter’s wedding. And she later filed a sworn statement in a civil suit that she turned over all work-related emails in her possession.

FBI Director James B. Comey said the FBI was able during its investigation to recover several thousand work-related emails Clinton had not turned over but said there was no evidence she purposely failed to do so.

Trump retreated from his statement Thursday, saying he was merely being “sarcastic,” but not before his provocative comment was criticized in Washington and denounced at the Democratic convention.

The Fix's Chris Cillizza explains why Donald Trump made a mistake when he called on Russia to find Hillary Clinton's missing emails. (Peter Stevenson/The Washington Post)

Some current and former U.S. intelligence officials have also expressed concern about Clinton, who was recently reprimanded by Comey for her “careless” handling of sensitive material in the emails. But unlike Trump, Clinton has participated in hundreds of intelligence briefings in her career and had access to classified material while working in the White House and the Senate.

The practice of briefing presidential candidates after conventions dates back decades, and typically involves — at least initially — sharing broad assessments of foreign events and threats.

Clapper said that the White House in the coming days would contact the Trump and Clinton campaigns, offering “fairly general” overviews on issues including the threat posed by the Islamic State and other terror groups.

Only the winner of the election in November will be given a detailed briefing on the most sensitive U.S. secrets, including clandestine CIA operations and capabilities overseas.

Clapper emphasized that candidates are free to decline briefings. The U.S. official who spoke anonymously said he believes Trump might do so. “It’s entirely conceivable that he will say, ‘I know all that. I don't want to be briefed,’ ” the official said.

Clapper, who is nearing the end of a half-century career in the intelligence community, spoke cautiously about the presidential campaign, carefully avoiding any explicit mention of Trump. Even so, Clapper seemed to struggle to completely conceal his views during an appearance at the Aspen Security Forum.

Possibly alluding to Trump’s statement that he would not feel bound to protect NATO allies, Clapper said that his counterparts in foreign governments have paid close attention to such campaign rhetoric and that “it is a worry to them.”

Asked how he responds to such concerns abroad, Clapper said, “I tell them that I appreciate them sharing their concerns, that it is our process in the United States, and hopefully it will all come out right.”

Rosalind S. Helderman contributed to this report.