The announcement on Wednesday comes a day after Eneos and Osaka Gas said they would study construction of a large e-methane facility - based on green hydrogen - and to be located in the Osaka Bay area.

The four companies would study options for receiving, storing and supplying ammonia - which can be used in power generation among other fields - in the Osaka area to potentially expand its usage in the Kansai and nearby Setouchi regions.

Hydrogen and ammonia, which do not emit CO2 when burning, are an important part of Japan's energy security strategy to reduce usage of traditional fossil fuels. Mitsui is Japan's biggest ammonia importer.

(Reporting by Katya Golubkova; Editing by Rashmi Aich)