Treasury Secretary Steven Mnuchin will brief lawmakers Thursday on the Treasury Department's decision to ease sanctions on companies linked to a Russian oligarch, House Speaker Nancy Pelosi's office confirmed Wednesday.

The briefing with the House Foreign Affairs Committee was scheduled after seven Democratic committee chairs requested to know why the department announced last month that it would lift penalties against aluminum manufacturing giant Rusal and two other companies connected to Oleg Deripaska. Mnuchin says Deripaska would remain blacklisted as part of sanctions targeting Russian business executives, but that the companies had committed to "significantly diminish Deripaska's ownership and sever his control."

The Democratic letter said the agreement appeared to allow Deripaska to keep "significant ownership" of one of the companies, the energy-related holding company EN+ Group, and requested the briefing "to allow for a full discussion of the agreement, the sanctions termination, and the impact that these decisions would have on the U.S. effort to end Russia's malign activities aimed at our country."

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Deripaska has emerged as a player in Special Counsel Robert Mueller's investigation over his ties to Trump's former campaign manager Paul Manafort. Deripaska, a close ally of Russian President Vladimir Putin, signed a $10 million annual contract with Manafort in 2006 and the two maintained a business relationship until at least 2009.

Also Wednesday, House Judiciary Committee Chairman Jerrold Nadler, D-N.Y., rejected Acting Attorney General Matthew Whitaker's offer to testify before the panel next month, instead insisting that Whitaker appear no later than Jan. 29 -- the day President Trump is scheduled to deliver the State of the Union address before Congress.

"As you know, it has been nearly 15 months since [former] Attorney General [Jeff] Sessions testified before the Committee," Nadler wrote. "It is past time for the Committee to conduct oversight of the Department."

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Whitaker had previously suggested to Nadler that he testify on Feb. 12 or Feb. 13, provided that "the Department is at least two weeks removed from a partial government shutdown." Nadler responded: "I cannot accept your proposal," saying that Whitaker's testimony was needed "on a number of pressing matters."

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According to Nadler, those matters included "several apparently false statements by administration officials about national security threats at the southern border" and "the impact of President [Trump]'s near-daily statements attacking the integrity of the Department of Justice, the FBI, and Special Counsel Robert Mueller's investigation."

In addition, Nadler wrote, Whitaker will likely face questions about his refusal to recuse himself from overseeing the Mueller probe.

The Associated Press contributed to this report.