The new target is far more ambitious than the eight-percent reduction advocated by the outgoing conservative government of Prime Minister Taro Aso, which lost parliamentary elections on August 30.

“As a mid-term goal, we aim at a 25 percent reduction by 2020 from 1990, based on the levels demanded by science to stop global warming,” said Hatoyama, who is due to take over as prime minister on September 16.

“Our nation will strongly call on major countries around the world to set aggressive goals,” added Hatoyama, 62, who last week suggested that Japan would seek a greater voice in international diplomacy.

Hatoyama, head of the Democratic Party of Japan (DPJ), made clear that Japan would ask other major emitters also to set tough targets, saying that “climate change cannot be stopped if only our country sets a reduction target.”

“A highly ambitious accord with participation by all major countries is a prerequisite to our country's promise to the international community,” he said.

Japan, the world's second largest economy, would formally present its goal at international talks in Copenhagen in December aimed at agreeing a follow-up treaty to the Kyoto Protocol, which expires in 2012.

Under the Kyoto Protocol, Japan pledged a six percent cut from 1990 levels by 2012 — but emissions in Asia's largest economy have instead risen by 8.7 percent since then.

The country's largest industrial lobby, Keidanren, has pushed for a new reduction target of no more than six percent.

Yvo de Boer, the chief of the U.N. Framework Convention on Climate Change, which preceded the Kyoto protocol, called the DPJ's new target “laudable.”

He said “it is commensurate with what science says is needed and will catalyze real change in the Japanese economy.”

“With such a target Japan will take on the leadership role that industrialized countries have agreed to take on climate change abatement,” de Boer told the Asahi World Environment Forum conference in Tokyo.

Japan is the world's fifth largest emitter of greenhouse gases, which are blamed for raising global temperatures, melting the earth's ice caps and glaciers, and changing weather patterns.

Outgoing prime minister Aso in June announced a far lower greenhouse gas reduction target, equivalent to eight percent from 1990 levels by 2020, earning his government strong criticism from environmental groups.

Hatoyama said: “I hope that a power shift in Japan will lead to a big change in climate change measures and mark the beginning of a big contribution to the future of our society in international negotiations.”

Without mentioning China or India by name, Hatoyama said: “We think developing countries are also required to make an effort to reduce greenhouse gases, as a global effort is needed on the issue of climate change.”

“Developed countries should provide financial and technical support for developing countries that are trying to reduce greenhouse gases.”

De Boer said the world had no time to waste.

“At the international level, it has become a well-known fact that a strong international deal to combat climate change needs to be sealed at Copenhagen this December,” he said.

“An ambitious deal is an unequivocal requirement to stop climate change from slipping out of control.”

He stressed that “Copenhagen is about more than an agreement on climate change. It is a litmus test for a new age of multilateralism.”