A Justice Department investigation of two prominent lobbyists that was spun off from special counsel Robert Mueller's Russia probe has concluded without charges, people familiar with the matter said Tuesday.

The Justice Department recently informed lawyers for Tony Podesta and former Rep. Vin Weber that they had ended the investigation into unregistered lobbying for pro-Russia Ukrainian interests. That work had come under scrutiny first by Mueller and later by federal prosecutors in New York, which late last year reached out to lawyers for potential witnesses in a sign of investigative activity.

"I have been notified that the investigation relating to Vin Weber is over," Robert Trout, a lawyer for Weber, said in a statement Tuesday. "As we have previously stated, at all times Mr. Weber acted in good faith and in keeping with the legal advice his company received from its outside counsel. We are obviously pleased by this development."

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The lobbying firms became entangled in Mueller's investigation as prosecutors examined the business dealings of Donald Trump's former campaign chairman, Paul Manafort, who worked with the companies as part of a lucrative lobbying effort he directed on behalf of former Ukraine President Viktor Yanukovych.

Podesta is a longtime Democratic operative whose brother, John Podesta, ran Democrat Hillary Clinton's 2016 presidential campaign. He stepped down in 2017 as chairman of his firm, and it shut down soon after. Weber is a former Republican congressman from Minnesota.

The investigation coincided with a Justice Department crackdown on unregistered foreign lobbying. Under federal law, U.S. lobbyists must declare publicly if they represent foreign leaders or their political parties and provide detailed reports about their actions to the Justice Department.

The conclusion of the investigation, first reported by The Washington Post, underscores the difficulties prosecutors face in conducting criminal probes related to the Foreign Agents Registration Act.

Prominent Washington lawyer Greg Craig, a White House counsel in the Obama administration, was acquitted this month on allegations that he misrepresented his role in his law firm's report on behalf of Ukraine's government. Separately Tuesday, a federal judge in Virginia threw out the convictions of a business partner of former Trump national security adviser Michael Flynn who'd been accused of acting as a foreign agent for Turkey.

A spokesman for the U.S. attorney's office in Manhattan declined to comment.