The US last month imposed sanctions on Oleg Derispaska and several companies in which he is a major shareholder including Rusal, EN+ and vehicle manufacturer Gaz Group. Deripaska’s En+ Group holds his 48% stake in Rusal, Russia's largest aluminium producer.

The deadline for divestiture has been extended to June 6 from May 7, according to the statement.

This extension follows a similar announcement from the US Treasury on April 23 that it would give US businesses until October 23 - instead of June 5 - to wind down dealings with Rusal.

In late April, Deripaska agreed to reduce his stake in Rusal’s main shareholder EN+ Group.

The recent loosening of the sanctions has given rise to bearish sentiment toward aluminium premiums because it is seen as allowing Rusal more time to sort out its entanglement with Deripaska and find a way to continue selling into the US.

The US Midwest aluminium premium eased to 21.5-22.5 cents per lb on Tuesday, from 22-22.5 cents per lb on April 27. The premium had recently been at a three-year high of 22-23 cents per lb – a level which it had held from April 10-24.