Twenty of the world's top polluting nations have agreed to discuss binding targets for reducing greenhouse gas emissions, Germany's environment minister said on Tuesday.

Sigmar Gabriel told a news conference during climate talks in Berlin that all involved, including the United States, had shown willingness to discuss targets proposed by the United Nations special envoy on climate change.

"We agreed...that unequivocally the central task for Bali will be to discuss...these measures," Gabriel said, referring to U.N. climate talks scheduled for Bali, Indonesia, in December.

U.N. climate envoy Ricardo Lagos told the Berlin meeting of energy and environment ministers that developed countries should aim to reduce emissions by 30 percent by 2020 and 60 percent by 2050 compared to 1990 levels.

Industrializing countries like India and China currently outside the Kyoto Protocol would have a separate target of achieving 30 percent greater energy efficiency by 2020.

The proposals will form the basis for the Bali meeting where ministers hope to discuss a successor agreement to the Kyoto Protocol on cutting harmful emissions. The Protocol expires in 2012.

U.S. President George W. Bush has so far refused to sign up to numerical targets before rising powers like China and India make similar pledges.

Ahead of the Bali conference, Bush has called a meeting of major emitting countries in Washington for September 27-28 to work out future cuts. It remains unclear how that meeting will fit into the broader U.N. efforts.

Gabriel reiterated that the U.S. climate talks must not attempt to distract nations from Bali but have to be "under the umbrella of the United Nations."

He also said that the United States, like India and China, was under pressure and would eventually have to agree to binding goals that can be verified. Washington could not, he said, ignore "the elephant in the room."

The 2-day Berlin talks, which included representatives from the Group of Eight club of industrialized nations (G8), China and India, confirmed that the new climate deal should be decided by the end of 2009 as it would take about two years to ratify.

Gabriel said the Berlin talks were "the starting point for the dialogue marathon in Bali."

Although Bush has agreed to discuss targets, the United States and other top polluters disagree widely about how deep any long-term cuts in carbon dioxide emissions should be.