The UK government is attempting to block the $6.5 billion purchase of oil and gas company RWE Dea by Russian billionaire Mikhail Fridman, citing the restrictions placed on oil and gas deals by the EU sanctions against Russia.

RWE Dea is the oil and gas subsidiary of Germany-based RWE.

The deal could either be delayed or scrapped altogether, the Financial Times said.

LetterOne, Fridman’s Luxembourg-based investment fund, announced its intention to purchase RWE Dea in March prior to the UK’s adoption of sanctions against Russia.

The fund was established in 2013 by Fridman and German Kahn to invest $14 billion in proceeds the duo earned when they sold off their stake in Russian oil company TNK-BP to Rosneft.

The RWE Dea sale was approved by the German government in August.

However, because RWE Dea operates in the UK LetterOne must receive a “letter of comfort” stating that the UK government does not object to the deal.

Last month, RWE said it was “uncertain” if the deal would receive UK approval.

LetterOne and RWE reportedly want the UK government to agree not to seize and sell off the UK North Sea assets included in the deal if the UK winds up adopting stricter sanctions against Russia, the Financial Times said.

LetterOne said it is currently discussing the deal with the UK Department of Energy and Climate Change.

RWE said it is still working to close the deal in 2014.