LONDON (Reuters) - The aluminium empire of Russian magnate Oleg Deripaska is in close contact with the U.S. Treasury, but needs until mid-summer to come up with a plan to meet U.S. requirements to escape sanctions, the chairman of its holding company told Reuters.

FILE PHOTO: Oleg Deripaska, En+ Group's major shareholder, attends an agreement signing ceremony with the Krasnoyarsk region's government, in Moscow, Russia December 12, 2017. REUTERS/Sergei Karpukhin/File Photo

The U.S. Treasury in April imposed sanctions against billionaire Deripaska and the eight companies in which he is a large shareholder, including the world’s second largest aluminium producer Rusal, in response to what it called “malign activities” by Russia.

Following pressure to soften its stance from business groups, Washington suggested it might lift the sanctions against Rusal and parent En+ if Deripaska cut his En+ stake to below 50 percent and introduced independent board members.

Under the current sanctions, U.S. businesses need to wind down aluminium trading with Rusal by October, while trading in Rusal’s and En+’s shares and debt should be discontinued by June 5.

The U.S. Treasury Department gave Rusal a reprieve on Thursday by extending the divestiture deadline to Aug. 5.

En+ Chairman Greg Barker told Reuters he had asked the U.S. Treasury to extend the licence to carry on trading the shares until September while he works on a plan to get En+ and Rusal off the sanctions list.

“We are seeking an extension of the general licence to allow us the time to put together the remaining building blocs in order to present a finalised proposal to the U.S. government by mid-summer,” Barker said in a phone interview.

Deripaska controls 66 percent of En+, which in turn controls 48 percent of Rusal. Discussions over reducing Deripaska’s stake could be complicated by the fact his ex-wife Polina also controls 5.8 percent of En+.

Barker, who met Irish Business Minister Heather Humphreys on Thursday, is seeking the support of Ireland to persuade the Treasury to back the plan.

“The Irish government has been very engaged with Rusal to find ways in which they can mitigate the impact of sanctions. I will be going (to Dublin) with a very clear message,” he told Reuters on Wednesday.

Rusal is the parent company of Aughinish Alumina in County Limerick, Ireland, which employs around 450 workers. The Askeaton-based company refines imported bauxite into alumina which is a major ingredient in the manufacturing of aluminium.