Japanese Prime Minister Kishida Fumio spoke to reporters after the G20 summit ended on Sunday in India.
He said it was significant that the declaration was adopted despite the widening gap over Russia's invasion of Ukraine.
Kishida said, "It was a major outcome for all the G20 nations to agree in the declaration that member countries firmly maintain the principles of the United Nations' Charter regarding Ukraine, which include fair and permanent peace, territorial integrity and sovereignty."
Kishida also talked about the discharge of treated and diluted water from the crippled Fukushima Daiichi nuclear plant. He said he had gained further support from the world's leaders by explaining the safety of the release of the treated water.
He said they had evaluated the process of discharging the treated water as safe and transparent.
Kishida said, "I could gain support and understanding for Japan's measures from the US, Australia, Indonesia, Malaysia and the Cook Islands, which chairs the Pacific Islands Forum. Other countries such as Turkey and the Netherlands also showed their support."
Kishida mentioned his brief meeting with China's Premier Li Qiang. China strongly opposes the water release and has suspended imports of Japanese seafood products.
Kishida said he will continue to seek the early retraction of China's measure by using various opportunities through commercial frameworks such as regional comprehensive economic cooperation.
The prime minister also said that he intends to reshuffle his Cabinet and executives of the main ruling Liberal Democratic Party as early as Wednesday.