A unit of Tokyo Gas is in advanced talks to buy U.S. natural gas producer Rockcliff Energy from private equity firm Quantum Energy Partners for about $4.6 billion, including debt, people familiar with the matter said on Tuesday.

If consummated, the deal would be the latest move by a Japanese entity to secure gas in jurisdictions perceived as friendly, the importance of which has risen for the import-dependent Asian nation after supply markets for the commodity were roiled by Russia's invasion of Ukraine.

The all-cash deal with Houston-based TG Natural Resources, which is 70% owned by the Japanese energy firm, is set to be announced this month, the sources said, requesting anonymity as the discussions are confidential. Castleton Commodities International (CCI) owns the rest of TG Natural Resources.