A firm hired by the U.S.Treasury Department is auditing Russian aluminum giant Rusal to check whether it is complying with the terms of a deal under which Washington agreed to lift sanctions on the company, Rusal said.

The audit is the first glimpse of how Treasury is policing whether Rusal and its parent company En+ are adhering to the deal — in particular the stipulation that Russian oligarch Oleg Deripaska’s control over the business be severed.

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A source familiar with the situation said the audit included checks on the telephone and email records of a small circle of Rusal senior executives and board members to establish whether they remained in contact with Deripaska, who is himself still on a U.S. sanctions blacklist.

There was no word from Rusal or sources familiar with the situation on whether the audit had found anything that might be at odds with the deal on lifting sanctions.

In reply to Reuters questions about the Treasury Department’s Office of Foreign Assets Control (OFAC) inspecting Rusal’s offices, the company issued a statement saying: “These are not checks by OFAC but an audit which was agreed as part of conditions for lifting of sanctions.”

A firm hired by the U.S. authorities is conducting the audit, Rusal said, giving no further detail. OFAC did not reply to a Reuters request for comment.