Federal prosecutors from the Southern District of New York confirmed Thursday that two associates of Rudy Giuliani, President Donald Trump's personal lawyer, were taken into custody.

The two Soviet-born men, Lev Parnas and Igor Fruman, were charged with violating campaign-finance laws late Wednesday, The Wall Street Journal reported.

Parnas and Fruman took an active role in helping Giuliani dig up dirt on former Vice President Joe Biden and his son ahead of the 2020 election, prosecutors say.

The two men are expected to appear in federal court on Thursday.

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A spokesperson for the Southern District of New York confirmed on Thursday that two associates of President Donald Trump's personal attorney, Rudy Giuliani, were taken into custody as part of an ongoing federal criminal investigation.

Prosecutors say the men have helped Giuliani dig up dirt on former Vice President Joe Biden, and have been arrested and charged with violating campaign-finance laws, The Wall Street Journal reported.

The two men, Lev Parnas and Igor Fruman, are Soviet-born and were under investigation by federal prosecutors in the Southern District of New York. They are expected to appear in federal court in Virginia on Thursday, the report said.

It's unclear what the charges against them entail and what they are specifically accused of doing.

The Journal reported that both Parnas and Fruman have donated to Republican campaigns and gave $325,000 to the main pro-Trump super PAC, America First Action, in May 2018, through a company called Global Energy Producers.

The Campaign Legal Center flagged the donation in a complaint with the Federal Election Commission in July 2018 and asked the panel to investigate whether Parnas and Fruman broke election law by trying to conceal the source of their donation.

Read more: A Fox News poll found that more than half of American voters want Trump impeached and removed from office

According to The Journal, Parnas and Fruman also aided Giuliani in his efforts to encourage Ukrainian officials to investigate Biden and his son Hunter's business dealings. The two men are being represented by John Dowd, who served as Trump's personal defense lawyer during the FBI's Russia investigation.

Trump and Giuliani's efforts to pressure Ukraine to investigate the Bidens were at the center of an explosive whistleblower complaint that a US intelligence official filed against Trump in August. Among other things, the complainant alleged that the president abused his power to "solicit interference from a foreign country in the 2020 US election" during a July 25 phone call with Ukrainian President Volodymyr Zelensky.

Giuliani was mentioned 31 times in the complaint and is described as a "central figure" in Trump's effort. The complaint said Attorney General William Barr "appears to be involved as well."

Giuliani is a private citizen, but the complaint lists multiple instances of the president's attorney working with US government officials and Ukrainian officials to solicit dirt on the Bidens for Trump's political benefit.

Giuliani has said that he got involved in Trump's efforts only after State Department officials asked him to do so. Text messages between several top US diplomats and Giuliani that were released last week confirmed Giuliani's claim.

The whistleblower's complaint is at the heart of a brewing congressional impeachment inquiry looking at whether Trump used his public office for private gain. House Democrats sent out a flurry of subpoenas and document requests, but the White House said earlier this week that it would not cooperate with what it views as a "partisan and unconstitutional" process.