WASHINGTON — The FBI was investigating former Trump national security adviser Michael Flynn as recently as December, a high-level US intelligence official has told BuzzFeed News.

The bureau was prepared to close the investigation into Flynn until “the Logan Act stuff,” the official said, referring to phone calls in late December where Flynn reportedly discussed US sanctions with Russian ambassador Sergey Kislyak.

The source brought up the Flynn investigation after BuzzFeed News asked if clear evidence existed tying Trump to Moscow. The official then mentioned the FBI investigation into Flynn. It was not clear if the FBI’s probe was a counterintelligence investigation.

Flynn’s phone calls with Kislyak, first reported by the Washington Post, were a potential violation of the Logan Act, which forbids private citizens from negotiating with foreign governments. At the time of the calls with Kislyak, the Trump team had not yet taken over the US government, and Flynn had yet to take up his new public official role. The Logan Act has never been used to prosecute anyone.

That an investigation was already up and running in December indicates there was concern among the intelligence community about Flynn’s loyalties before his phone calls with Kislyak. After the nature of those calls was revealed by the Post in January, Flynn quickly left the White House for misrepresenting the nature of the calls to Vice President Mike Pence.

It remains unknown when the FBI first started investigating Flynn and whether the probe has since been closed. In addition to fostering ties with Moscow — a longtime commentator on the Kremlin’s state-run news channel Russia Today, Flynn dined with Russian President Vladimir Putin during a trip to Moscow in 2015 — Flynn was also retained by a Turkish lobbying firm, a position he maintained while serving as Trump’s confidant.

Flynn, whose security clearance was only recently revoked, maintained access to classified information throughout the course of the campaign. The FBI investigation remained open at least until December, according to the intelligence official, at which point Flynn — who was named as Trump’s pick for national security adviser in November — was attending high-level national security briefings and accessing classified information.

Rumors have shot through Washington for months about whether the FBI was openly investigating Trump or any of his associates as a counterintelligence threat.

FBI Director James Comey was expected to address those rumors Wednesday, after reportedly promising lawmakers that after months of speculation he would publicly address whether the Trump campaign was under investigation by the bureau. But lawmakers backtracked Wednesday, and said Comey had never promised to publicly clarify questions about Trump and the FBI.

The FBI declined to comment. Neither the White House nor Flynn immediately responded to a request for comment.

