Exxon Mobil Corp. has notified Russian officials it will sue the federal government unless Moscow allows the company to exit a major oil and gas project, the Wall Street Journal reported https://www.wsj.com/articles/exxon-escalates-dispute-with-russia-over-barred-exit-from-giant-oil-project-11661851802?mod=latest_headlines on Tuesday, citing people familiar with the matter.

Russia has banned investors from so-called unfriendly countries from selling shares in key energy projects and banks in the nation until the end of the year, stepping up pressure in the sanctions stand-off with the West.

The ban covers almost all big financial and energy projects where foreign investors still have stakes, including the Sakhalin-1 oil and gas project, in which U.S. oil major Exxon holds a 30% stake.

Exxon's spokesperson Casey Norton confirmed the company had sent the Russian government a notice of difference.

"Exiting is a complex process, and as the operator, we must protect the safety of employees, the environment, and the operation," Norton said.