The Washington offices of international law firm Skadden Arps Slate Meagher & Flom LLP are seen in downtown Washington, U.S., February 20, 2018. REUTERS/Jonathan Ernst

WASHINGTON (Reuters) - A prominent New York law firm whose work has come under scrutiny in U.S. Special Counsel Robert Mueller’s Russia probe reached a settlement with federal prosecutors on Thursday, acknowledging it should have registered as a foreign agent for a 2012 report aimed at discrediting a former prime minister of Ukraine.

Skadden, Arps, Slate, Meagher & Flom LLP agreed to turn over $4.6 million, the amount it was paid for the report, and retroactively register as a foreign agent as part of the deal with the U.S. Justice Department.

The department said in a press release that a Skadden Arps partner in 2012 and 2013 had provided “false and misleading” statements about its work on the report, masking the true nature of its client and hiding from the public “that its report was part of a Ukrainian foreign influence campaign.”

One former Skadden lawyer, Alex van der Zwaan, has already been caught up in Mueller’s probe. He served 30 days in prison last year for lying to FBI agents in a case focused on his work on the report for Paul Manafort and Rick Gates, who were senior officials in Donald Trump’s 2016 U.S. presidential election campaign.

“The civil settlement announced today brings the firm closure with the U.S. government regarding issues relating to a report we produced for the Government of Ukraine in 2012,” Skadden, Arps said in a statement.

“We have learned much from this incident and are taking steps to prevent anything similar from happening again.”

Manafort, who helped promote the report to journalists and others in the United States, has pleaded guilty to undisclosed lobbying work for pro-Russian politicians in Kiev, including then Ukrainian President Viktor Yanukovych, among other crimes.

The Skadden report examined efforts by the Ukrainian government to prosecute Yulia Tymoshenko, the country’s former head of government who was convicted in 2011 of embezzlement and corruption charges and sentenced to seven years in prison.

Yanukovych’s government used the report to justify to the European Court of Human Rights Tymoshenko’s pretrial detention.