"It's going to be very difficult" to renew Kyoto, he said, adding there was such a wide range of views among participants on tackling global warming that it would be difficult for them to reach any consensus beyond 2012.

Kyoto entered into force on Feb. 16 despite a US pullout and has backing from 150 countries.

Under Kyoto, rich nations are meant to cut emissions of heat-trapping carbon dioxide -- largely from burning fossil fuels in factories, power plants and cars -- by 5.2 percent below 1990 levels by 2008-12.

Many delegates hailed the Bonn talks for allowing them to discuss ideas about how to rein in emissions, blamed for nudging up world temperatures that could trigger increasing disruptions ranging from storms to droughts by 2100.

"I was pleasantly surprised by the willingness of the major players to engage in discussions about policies," said Japan's Masaki Konishi, who co-chaired the talks.

"A BABY STEP"

Environmentalists praised South Africa, China, Argentina and Mexico for outlining policies to fight climate change and said the Bonn talks were a good first step towards widening Kyoto to include developing nations.

"This is a baby step, but an important one," said Jennifer Morgan, director of the WWF's climate change programme.

Even so, many developing nations said rich nations were failing to stick to their own commitments for cuts in emissions and were failing to provide aid and new technologies to help the poor shift to clean energies like wind or solar power.

Watson said Washington had no plans to sign up for Kyoto-style caps on carbon dioxide even though he said that US emissions dipped in 2003 below 2000 levels.

"It's hard to imagine that emissions will not increase again," he said, pointing to economic growth and a rising population. The US senate has in the past rejected proposals to cap US emissions at 2000 levels.

US President George W. Bush pulled out of Kyoto in 2001, saying it was too costly and wrongly excluded developing nations from the first period. He also said more research was needed.

US climate policy focuses on cutting the amount of carbon emitted per dollar of gross domestic product by 18 percent in the decade to 2012.

But Greenpeace's climate expert Steve Sawyer predicted that pressure from the public, businesses and the international community would eventually lead the United States and Australia -- the outsiders among rich nations -- to join up.

Earlier, Joke Waller-Hunter, executive secretary of the UN Framework Convention on Climate Change, faulted states including Spain, Greece and Ireland for failing to rein in emissions.

"There are a number of countries ... that are far from their targets," she told Reuters. She expressed hopes that a meeting of environment ministers in Montreal, Canada, in December would map out what needed to be done to renew and extend Kyoto.