CEFC China Energy is in talks to make an investment in Russia’s state-controlled oil company Rosneft, in what would be a sign of strengthening economic co-operation between Moscow and Beijing even as relations with the US deteriorate.

CEFC, a private conglomerate with interests in the energy and financial services industries, has been negotiating a deal to invest in the world’s largest publicly listed oil producer that could be announced as soon as this week, according to four people with knowledge of the talks.

If agreed, the complex deal would mark a growing corporate relationship between China and Russia that has focused on cross-border energy deals. This has strengthened this year against the backdrop of increasingly acrimonious ties between Moscow and the west, involving sanctions levied against major Russian companies including Rosneft.