WASHINGTON — U.S. Treasury Secretary Steven Mnuchin, under fire from Democratic lawmakers, defended the proposed removal of Russian aluminum behemoth United Co. Rusal from the administration’s blacklist as evidence of a successful sanctions strategy.

Mnuchin briefed House lawmakers on Thursday on the Treasury Department’s plan to delist Rusal and two other companies owned by Oleg Deripaska, an ally of Russian President Vladimir Putin. Deripaska and, subsequently, his companies, were sanctioned last April in response to Moscow’s 2016 election interference and involvement in wars in Ukraine and Syria.

Several lawmakers questioned the plan, critical of the terms they say keeps the world’s second-largest aluminum producer under the Kremlin’s control, and have filed resolutions to reject the proposal.

Mnuchin reiterated in a statement ahead of the classified briefing that the plan keeps Deripaska himself on its blacklist and requires him to divest his majority stake in Rusal’s holding company, EN+ Group PLC and another Russian energy firm. “One of the goals of sanctions is to change behavior, and the proposed delistings of companies that Deripaska will no longer control show that sanctions can result in positive change,” Mnuchin said.

An expanded version of this report appears on WSJ.com.

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