Ukraine's ambassador to Japan says he expects a very strong message from the Group of Seven leaders to support Ukraine until its victory.

Sergiy Korsunsky was speaking in an interview with NHK in Tokyo on Thursday, a day before the G7 summit kicks off in Hiroshima.

With the Ukrainian situation a key topic on the first day of the talks, Korsunsky expressed hope for the role Japan will play as the chair country.

He said Prime Minister Kishida Fumio "has a very clear and strong vision of international order based on law and on rules, and we are very grateful and we very much appreciate the position of Japan."

The ambassador also expressed a strong sense of crisis about Russia's continuing nuclear threat to the world.

He said it's "very much unfortunate that this threat is real and we hear it all the time, endlessly that, particularly, they say that if we try to liberate occupied territories of Ukraine."

As for Ukraine's reconstruction efforts, Korsunsky expressed hope for further assistance from Japan, including its methodology for recovering from major natural disasters.

He said he also expects the business community to be encouraged to invest and take part in major efforts to rebuild Ukrainian infrastructure damaged by the Russian invasion.