Japan will impose additional sanctions against Russia after G7 leaders decided at their meeting in Hiroshima to step up punitive measures against Moscow over the Russian forces' invasion of Ukraine, Japanese government chief Hirokazu Matsuno said on Tuesday.

In addition, Matsuno, who is the government's chief spokesman, criticized Russia's deployment of tactical nuclear weapons in Belarus, saying it would further complicate the situation with the war in Ukraine.

"As the only country in the world against which nuclear bombings were carried out in wartime, we will never accept Russia's nuclear threats, much less the use of nuclear weapons," Matsuno told a regular news conference.

Japan, acting in coordination with other G7 countries, will freeze the assets of 78 organizations and 17 individuals in Russia.

In addition, Japan plans to ban the supply of construction and engineering services to Russia, with the details of the measure expected to be announced at a later date, the commerce ministry said in a statement.