Former Director of National Intelligence James Clapper said Sunday that he "can deny" that a warrant to wiretap Donald Trump or his associates was mounted to investigate possible ties between his campaign and Russia in the final months of the election.

"There was no such wiretap activity mounted against the president, the president-elect at the time, or as a candidate, or against his campaign," Clapper told Chuck Todd in an interview on Sunday's "Meet The Press."

Clapper and Todd were referring to Trump's tweets on Saturday morning that without evidence accused former President Barack Obama of having Trump Tower phones wiretapped before the election.

When Todd asked Clapper whether he could confirm or deny if a Foreign Intelligence Surveillance Act warrant had been granted to engage in this kind of wiretapping, Clapper said, "I can deny it."

Several national-security experts have said, however, that Todd's question was specific enough to leave Clapper some wiggle room in his response, which referred only to whether Trump campaign officials had been wiretapped.

Retired Gen. Michael Hayden, who has served as the director of both the National Security Agency and the CIA, said Monday morning that he viewed Clapper's response as a denial that Trump aides were specifically targeted by the FISA warrant — not as a denial that a warrant was granted to surveil foreign actors operating inside the US that might have been communicating with Trump aides.

A spokesman for Obama said Saturday that Obama never authorized a wiretap of Trump or any other American citizen and that "any suggestion otherwise is simply false."

On Monday morning, one of Trump's senior advisers, Kellyanne Conway, said former Obama administration officials who were denying that Trump Tower phones were tapped "also left the door open" to the possibility that they were. MSNBC's chief legal correspondent, Ari Melber, replied on Twitter that while former officials "aren't supposed to confirm a FISA warrant anyway," it is true that Obama's spokesman said the former president was not involved — not that there weren't any wiretaps.

FBI Director James Comey on Sunday reportedly asked the Department of Justice to refute Trump's accusations. Matthew Miller, the department spokesman under the Obama administration, said Comey "would know beyond a shadow of a doubt whether there was wiretapping of Trump or his campaign."

"If he says there wasn't any, it's safe to say there wasn't," he told Business Insider.

The Justice Department has not yet issued a statement, but the president does not have the unilateral authority to order a wiretap on suspected foreign spies operating inside the US. Doing so would be a "massive crime," Miller said, that would implicate career civil servants and necessitate a huge cover-up.

Rather, law enforcement and intelligence agencies wishing to monitor signal intelligence they deem relevant to an investigation — in this case, Russia's interference in the 2016 election — must obtain a warrant from the Foreign Intelligence Surveillance Court. Such a process is authorized under the 1978 Foreign Intelligence Surveillance Act.

"Usually, the Department of Justice wouldn't comment on an ongoing investigation, but in a situation like this, where the president has questioned whether the department has violated federal law, is certainly in their interest to correct the record," Miller said. "If Trump's accusation were true, it would mean career civil servants were also involved in a massive crime, and the department needs to come out publicly and defend itself so the public knows it acted appropriately."

Juliette Kayyem, a national-security expert who served in the Department of Homeland Security and now teaches at the Harvard Kennedy School of Government, said on Twitter that "it can be both true" that someone is not the subject of a FISA wiretap but has their communications picked up by one.

"Once when getting security clearance, I learned my conversations had been picked up in FISA wiretap. I was talking w/ someone who had a wiretap on them," Kayyem said. "Nature of my work so wasn't shocking that I talked to [someone] who have ties to foreign intel investigation. Shows that comms are picked up on people not subject of wiretap."

Reports have suggested that communications between Trump's former national security adviser, Michael Flynn, and Russia's ambassador to the US, Sergey Kislyak, were picked up by US intelligence officials who had been eavesdropping on Kislyak — not on Flynn. Current and former US officials have also told several media outlets that they have intercepted communications between associates of Trump and Russian officials.

HeatStreet, The Guardian, the BBC, and McClatchy have reported various versions of the same story over the past three months: The FBI sought a warrant from the FISC to investigate evidence of improper communication between Russian nationals and associates of Trump during his presidential campaign.

It has not been confirmed that the FISA warrant targeted Trump associates or that it was ever granted. FISA warrants are rarely denied, however.

White House spokeswoman Sarah Huckabee Sanders said Sunday that the administration, in calling for an investigation into the accusations that Obama wiretapped phones in Trump Tower, was acting on media reports. But no news outlet has reported that Trump Tower had been wiretapped or that Obama had ordered it — except for Breitbart, the far-right website that was until recently helmed by Trump's chief strategist, Steve Bannon.