"We exchanged views on how Tokyo and the City of London can collaborate in tackling sustainable finance as we face the global energy crisis," Koike told reporters after meeting Vincent Keaveny, the Lord Mayor of London, and financial experts including former Bank of Japan deputy governor Hiroshi Nakaso.

Tokyo's metropolitan government has been deepening its collaboration with the City of London since 2017 when Tokyo launched its bid to become a global financial hub.

Thursday's meeting focused on discussing initiatives on sustainable finance in light of the energy crisis.

"At this time the world is facing a serious challenge, as we see the inconceivable war in Ukraine taking place and its effects on the world, and in particular on the supply of energy," Keaveny said. "This makes it more important than ever that we accelerate a push towards renewable sources of energy."

Keaveny said they were focusing on the importance of voluntary carbon markets, while seeking greater coherence in global standards and the push for transition finance.

The position of Lord Mayor is a largely ceremonial one whose role is to represent and promote businesses in the City of London, the financial hub of the British capital. The position is quite separate to that of the directly elected London mayor, who oversees the running of the capital.

(Reporting by Tetsushi Kajimoto; Editing by Gareth Jones)