Japan's top city gas supplier Tokyo Gas is looking to add more U.S. natural gas assets, its president said on Monday, as it aims to expand its gas-related businesses in North America after its recent acquisition of a U.S. shale gas producer.

The Japanese company paid $2.7 billion to acquire Texas-based natural gas producer Rockcliff Energy in December and agreed to purchase a 49% stake in North American energy marketing and trading firm ARM Energy Trading in February.

"We would still consider investing in shale gas assets if we can acquire them at the appropriate price and in a competitive way," Tokyo Gas President Shinichi Sasayama told reporters on the sidelines of the Japan Energy Summit conference in Tokyo.