LONDON — The German utility RWE and a Russian-controlled investment company signaled on Sunday that they expected to complete a deal for the oil and gas subsidiary RWE Dea on Monday, despite objections from the British government.

L1 Energy, based in London and owned by the Russian billionaire Mikhail Fridman and partners, agreed last year to buy RWE Dea for 5 billion euros, or about $5.6 billion. Among RWE Dea’s prime holdings are a large North Sea natural gas field called Breagh and other British assets.

The British government has declined to bless the sale out of concern that Mr. Fridman or his company might become the target of expanded sanctions on the Russian energy industry stemming from the Ukraine conflict. Any additional sanctions might force the shutdown of those fields, creating safety and environmental risks, according to the government.

Britain’s Department of Energy and Climate Change, which regulates the oil industry, strongly reiterated these concerns over the weekend. The department said in a statement Saturday that Edward Davey, the energy minister, was “minded” to require L1 to sell the British assets to a more suitable operator if the deal did go through.