A key witness in special counsel Robert S. Mueller III’s investigation of Russian interference in the 2016 U.S. election has been indicted with seven others on charges of conspiring to funnel more than $3 million in illegal campaign contributions, the Justice Department announced.

George Nader, an adviser to the United Arab Emirates who acted as an intermediary for members of the Trump campaign seeking to forge contacts in the Middle East, was charged with conspiring to make conduit campaign contributions and related offenses as part of a 53-count indictment unsealed Tuesday in Washington, prosecutors said.

U.S. prosecutors also charged Ahmad “Andy” Khawaja, a Lebanese American businessman, with 35 counts related to allegations that he conspired with Nader to conceal the source of more than $3.5 million in campaign contributions directed to U.S. political committees associated with presidential candidates.

A statement released by the Justice Department did not name the committees or candidates. But federal donor records show that Khawaja is a major political contributor, who, since 2016, personally gave $3 million to Democratic candidates and groups — including $1 million to Priorities USA, the main super PAC supporting Hillary Clinton’s presidential campaign — and $1 million to President Trump’s inaugural fund.

An attorney for Nader, who has pleaded not guilty and is set to face trial in January in federal court in Alexandria, Va., on unrelated charges of transporting a 14-year-old boy for sexual activity, declined to comment.

An attorney for Khawaja did not respond to requests for comment.

According to a written statement by Assistant Attorney General Brian A. Benczkowski of the Justice Department’s criminal division and FBI Washington Field Office chief Timothy R. Slater, Nader, 60 and Khawaja, 48, were charged along with Roy Boulos, Rudy Dekermenjian, Mohammad “Moe” Diab, Rani El-Saadi, Stevan Hill and Thayne Whipple. The latter six were “charged with conspiring with Khawaja and each other to make conduit campaign contributions and conceal excessive contributions” and related offenses, U.S. authorities said.

Khawaja’s donations earned him access to Clinton during the 2016 campaign and a post-election Oval Office visit with Trump, the Associated Press reported in a 2018 investigation. At that time, Khawaja; the payment processing company he founded, Allied Wallet; and top executives had contributed at least $6 million to Democratic and Republican candidates and groups.

From March 2016 to January 2017, the indictment alleges, “Khawaja conspired with Nader to conceal the source of more than $3.5 million in campaign contributions” that appeared in the names of Khawaja, his wife and his company, but that in reality were funded by Nader. “As Khawaja and Nader arranged these payments, Nader allegedly reported to an official from a foreign government about his efforts to gain influence,” prosecutors said.

The indictment also alleges that, from March 2016 through 2018, Khawaja conspired with the others to conceal his excessive contributions, which totaled more than $1.8 million, to various political committees. Among other things, these contributions allegedly allowed Khawaja to host a private fundraiser for a presidential candidate in 2016 and a private fundraising dinner for an elected official in 2018.

The indictment also alleges that this summer, Khawaja obstructed a grand jury investigation by providing a “witness with false information about Nader and his connection to Khawaja’s company.”

The 64-page indictment laid out the sweeping scope of the alleged scheme, and the proximity it gave the defendants to individuals whose descriptions appear to match Clinton and Trump.

“It was a purpose of the conspiracy for Nader and Khawaja to use their access to Candidate 1 to gain favor with, and potential financial support from, the government of Foreign Country A,” stated the charging document, filed by public integrity section prosecutors with the Justice Department’s criminal division.

The indictment quotes an alleged encrypted message that Nader sent an official from Foreign Country A via WhatsApp after Khawaja contributed $275,000 and invited Nader to attend and April 16, 2016, event for presidential Candidate 1.

“Wonderful meeting with the Big Lady . . . Can’t wait to tell you about it,” Nader allegedly wrote, in an apparent reference to Clinton.

The indictment noted that political committees that received funding unwittingly submitted false disclosure reports and were presumably victims of the plot. Still, Hillary Clinton apparently attended numerous events, including small gatherings, with Nader, who on July 19, 2016, messaged the foreign official a photograph of him with Candidate 1’s spouse — an apparent reference to Bill Clinton — at Khawaja’s home.

The indictment referred glancingly to Trump, charging that after the election, “Khawaja caused Company A to contribute $1 million to the U.S. President-Elect’s inaugural committee.” Khawaja then obtained tickets and attended Trump’s January 2017 presidential inauguration with Nader and Dekermenjian as his guests.

In May, however, Khawaja, his company and two other senior company officers agreed to pay $110 million to settle charges that they participated in numerous scams, knowingly processing transactions for merchants engaging in frauds, the Federal Trade Commission announced.

The federal investigation stemmed in part from the Associated Press’s reporting that showed the company aided pornographers, debt collectors and offshore gamblers to access the international banking system, often through dummy foreign corporations and fake websites.

Earlier, in 2010, Khawaja and his U.S. and British companies forfeited $13.3 million seized by the FBI the previous year to resolve allegations by federal prosecutors in Manhattan that the funds were involved in money laundering in connection with illegal online gambling.

Khawaja in 2018 was appointed by Sen. Charles E. Schumer (D-N.Y.) to the U.S. Commission on International Religious Freedom, a bipartisan federal panel.

Separately, Trump’s nonprofit presidential inaugural committee remains under investigation by federal and state prosecutors. The U.S. attorney’s office for the Southern District of New York in February issued subpoenas to the inaugural committee, which raised a record $117 million. Prosecutors are investigating potential money laundering, bank fraud and illegal foreign donations connected to the committee, which said it is cooperating with the probe.

Nader was seen by Trump allies as a helpful operator for navigating politics in the Middle East. He attracted Mueller’s interest for helping arrange a meeting in the Seychelles in January 2017 between Erik Prince, a Trump supporter who founded the private security firm Blackwater, and a Russian official close to President Vladi­mir Putin.

Nader later visited the White House several times, meeting with senior advisers Stephen K. Bannon and Jared Kushner, who is also the president’s son-in-law, according to people familiar with his visits.

Nader came and left the country repeatedly while speaking to Mueller’s team last year. He was charged under seal in April 2018, and did not return to the country until this June, when he was arrested at John F. Kennedy International Airport in New York.

Correction: An earlier version of this story misstated the year Khawaja was appointed by Sen. Charles E. Schumer (D-N.Y.) to the U.S. Commission on International Religious Freedom. The appointment was in 2018.

Rosalind S. Helderman contributed to this report.