The United Nations called Monday on rich nations to forge a "Global Green New Deal" that puts the environment, climate change and poverty reduction at the heart of efforts to reboot the world economy.

Leaders from the Group of 20 nations, meeting in April, should commit at least one percent of gross domestic product over the next two years to slashing carbon emissions, the United Nations Environment Programme (UNEP) said in a report released at the opening of its world forum in Nairobi.

"Reviving the world economy is essential, but measures that focus soley on this objective will not achieve lasting success," the UNEP cautioned, invoking the US New Deal launched by Franklin Roosevelt in the 1930s.

"Unless new policy initiatives also address other global challenges -- reducing carbon dependency, protecting ecosystems and water resources, alleviating poverty -- their impact on averting future crises will be short-lived."

The world's most developed economies must take the lead by adopting national plans to slash their use of the fossil fuels -- oil, gas and coal -- that drive global warming, the report says.

Measures could include the elimination of fossil fuel subsidies worth hundreds of billions of dollars, and the development of carbon pricing, either through taxes or cap-and-trade schemes.

The G20's rapidly emerging economies such as China, India, Brazil, South Africa and Turkey "should aim, as far as possible" for the same one percent of GDP targets, the UNEP urged.

Poorer and developing nations cannot be expected to make the same carbon-cutting commitments, but should spend at least one percent of GDP on expanded access to clean water and sanitation for the poor, it said.

Twenty percent of people in the developing world lack sufficient clean water, and about half -- some 2.6 billion -- do not have basic sanitation.