A Russian oligarch with ties to former Trump campaign manager Paul Manafort Paul John ManafortBannon trial date set in alleged border wall scam Conspicuous by their absence from the Republican Convention Ukraine language in GOP platform underscores Trump tensions MORE offered to cooperate with congressional committees probing Russia's efforts to interfere in the election, but lawmakers declined to accept his conditions, The New York Times reported Friday.

Oleg Deripaska, an aluminum magnate in Russian President Vladimir Putin's inner circle, made the offer on the condition of full immunity, three congressional officials told the Times. Lawmakers reportedly declined his offer because it would cause problems for federal criminal investigators.

The FBI as well as the Senate and House Intelligence committees are probing whether the Trump campaign colluded with Russia during the 2016 presidential election, with investigations drawing scrutiny to Manafort.

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Deripaska worked with Manafort in the the mid-2000s, while the Republican strategist advised Moscow-backed politicians running for office in Ukraine.

In 2007, Manafort and Deripaska established an offshore fund as they looked to buy Ukrainian cable television and telecommunications assets, but the deal fell through, leading to a lawsuit, according to the Times.

The Associated Press reported in March that Manafort gave Deripaska a plan in 2005 that detailed moves that would “greatly benefit the Putin government,” by influencing both U.S. news coverage as well as politics — allegations Deripaska denied, and which led him to sue the news wire service for libel. The AP says it stands by its report.

Manafort has denied claims that his work for Deripaska attempted to benefit the Kremlin.

The Times reports that it is unclear whether the FBI aims to interview the Russian oligarch.

Lawyers at the firm representing Deripaska in the suit did not respond to the Time's request for comment. Adam Waldman, a Washington lobbyist representing Deripaska, also did not respond to the newspaper’s request for comment.

Updated: Tuesday, 1:34 p.m.