Japan became a UN member in 1956 under prime minister Ichiro Hatoyama, Yukio's grandfather.

'Japan can speak with the greatest persuasiveness in urging nuclear weapon-states towards nuclear disarmament and non-nuclear states to avoid the temptation to acquire nuclear weapons,' he said.

Hatoyama told the UN climate change summit Tuesday that Japan will reduce greenhouse gas emissions by 25 percent by 2020 at 1990 levels, which drew praise from the UN because it was the only country to announce such a plan.

'Japan announces such an ambitious pledge because it wishes to serve as a 'bridge' among countries with varied interests and to preserve the planet for future generations,' he said.

Japan is the second largest financial contributor to the UN, behind the US. It is seeking a permanent seat on the UN Security Council and expanded responsibilities in the UN administration.