Donald Trump has continued to insist that reports that Russia was offering bounties to Taliban-linked militants to kill US troops in Afghanistan are "fake news".
At the same time, national security adviser Robert O'Brien said officials had decided not to present the president with "unverified intelligence" on the matter.
But in a television interview, he revealed that options had been drawn up to present to Mr Trump if the allegations were corroborated.
"If this eventually becomes something that's proven, or something that we believe, we need to have options for the president to deal with the Russians," Mr O'Brien told Fox News' 'Fox & Friends'.
"I can tell you this, if this information turned out to be true, and now we may never know, but if it turned out to be true, we had options ready to go, and the president was ready to take strong action, as he always is."
The 'Washington Post' reported this week that White House officials were first informed in early 2019 of reports that Russia was offering bounties on US and coalition troops, but the information was deemed sketchy.
On Twitter, Mr Trump wrote: "This is all a made up Fake News Media Hoax started to slander me & the Republican Party."
"The Russia Bounty story is just another made up by Fake News tale," he went on, taking issue in particular with reports claiming that he had received briefings on intelligence about the alleged Russian bounties, but had taken no action. In an interview with Fox Business Network, Mr Trump carried on his "hoax" theme.
"I'm sure I don't see many things that they don't think rose to the occasion," he said. "This didn't rise to the occasion. And from what I hear - and I hear it pretty good - the intelligence people didn't even … believe it happened at all. I think it's a hoax by the newspapers and the Democrats."
House Speaker Nancy Pelosi slammed Mr Trump in an MSNBC interview on Wednesday, accusing him of a "dereliction of duty" and calling him "intellectually unprepared, personally unqualified and ethically unfit" for his office.
Ms Pelosi added: "Now he has undermined any credibility he may have had as commander-in-chief, if he could call a possible assault on our troops … by the Russians a hoax, without even wanting to read about it, learn more about it and make a really informed judgment about it."
She also called for increased sanctions on Russia.
During the Fox News interview, Mr O'Brien claimed leaks to the media about the episode have hampered US intelligence officials in determining what actually happened.
"It might be impossible to get to the bottom of it because someone decided to leak to hurt the president rather than uphold their obligations to the American people," he said.
People familiar with the matter noted to the 'Post' that information is sometimes withheld from Trump, who often reacts badly to reports he thinks might undermine what he considers his good relationship with Vladimir Putin.