"In many ways these are pioneers. Many had valuable ideas," he said on the sidelines of a climate change conference in Bonn, Germany.

Under the 1997 Kyoto Protocol, richer nations are allowed to fund projects such as wind farms and solar energy parks in developing countries and get credits towards their own goals of cutting emissions of carbon dioxide and other so-called greenhouse gases blamed for global warming.

Twelve projects were presented to the U.N. body. The answer on each occasion was no.

The backers of three projects in Brazil, a landfill plant in South Africa, a wind farm in Jamaica and a project in South Korea will, however, be able to resubmit revised applications at the end of June. The backers in each case argued they would reduce the emissions of greenhouse gases such as carbon dioxide.

"We have to answer the question: why would this not have happened anyway," said Christine Zumkeller, coordinator of the U.N's cooperative mechanisms programme.

A country with many fast-flowing rivers could, for example, argue it is helping the planet by building hydro-electric plants instead of burning fossil fuels, but regulators say that may not be a legitimate argument if the fossil fuel plant was not a viable alternative in the first place.

The debate is likely to increase in coming years if the Kyoto Protocol takes effect and if a U.N. climate change summit in Milan in December agrees to give richer nations credits for planting trees that absorb carbon dioxide.

Most industrial nations, with the notable exception of the United States, the world's largest polluter, have ratified the Kyoto Protocol, which seeks to reduce greenhouse gas emissions below 1990s levels by 2012.

Under a complex weighting system, it would take effect if Russia ratified it as it has pledged to do.

Greenhouse gases are widely blamed for global warming, which threatens to raise sea levels by melting polar ice caps and to exacerbate droughts and flooding.