Any Obama officials involved in Flynn 'unmasking' declassified: Source

Acting Director of National Intelligence Richard Grenell has declassified a list of former Obama administration officials who were allegedly involved in the so-called "unmasking" of former national security adviser Michael Flynn in his conversations with the former Russian ambassador during the presidential transition, a senior U.S. official tells ABC News.

Grenell, who remains the U.S. ambassador to Germany along with being the acting DNI, visited the Justice Department last week and brought the list with him, according to the official.

On Tuesday, a senior Justice Department official told ABC News that the department does not intend to release the list and deferred to the ODNI for any further comment.

Separately, the official said the department has been reviewing unmasking as part of U.S. attorney John Durham's broader review of the activities of investigators in 2016 and 2017 during the Russia probe.

"ODNI delivered information related to unmasking and we have taken note of it," the official said. "We will be looking at it to the extent that it is relevant to any investigation."

His visit indicates his focus on an issue previously highlighted in 2017 by skeptics of the investigation into the Trump campaign's contacts with Russia, specifically allegations that former officials improperly unveiled Flynn's identity from intercepts of his call with former Russian ambassador Sergey Kislyak.

Grenell's visit came the same week that Attorney General William Barr moved to dismiss the criminal case against Flynn following his guilty plea for lying to the FBI about his conversations with Kislyak.

Barr has said that new information revealed in recent weeks about the conduct of FBI officials involved in the interview of Flynn showed that their investigation was not "legitimate."

"They did not have a basis for a counterintelligence investigation against Flynn at that stage, based on a perfectly legitimate and appropriate call he made as a member of the transition," Barr said in an interview with CBS last week.

Critics, including nearly 2,000 former DOJ officials, have argued the move was part of a pattern of Barr looking to undermine an investigation that was politically damaging for President Donald Trump. The officials called for Barr to resign over his intervention in the case.

In May 2019, Trump empowered Barr with declassification authority for his broader investigation into the Russia probe.

While the law requires that identifying information of U.S. persons picked up during foreign surveillance be "masked," high-ranking intelligence officials can request the identities be revealed if they feel the information is necessary to further understand the intercepts.

Former Obama national security adviser Susan Rice has openly acknowledged unmasking the identities of some senior Trump officials during the presidential transition but has strenuously denied ever leaking any identities and said nothing she did was politically motivated.

In 2017, Rep. Devin Nunes -- a longtime critic of the Russia investigation -- accused the Obama administration of improper unmasking of Trump transition officials after he secretly met with two national security officials at the White House who he said provided him with documents supporting his assertions.

Trump at the time incorrectly stated that Nunes' findings confirmed his still-unfounded claims that President Barack Obama wiretapped his campaign at Trump Tower in 2016.

To date, however, Nunes has not provided any evidence backing up his accusations or showing that Obama officials were politically motivated in their unmasking of Trump transition officials.

ABC News' Alexander Mallin contributed to this report.