The United States on Monday rejected a proposal to include 25- to 40-per cent reductions in greenhouse gas emissions by 2020 in a UN draft agreement at a climate change conference.

To agree to greenhouse gas reductions would require "a lot of analysis," said Harlan Watson, head of the US delegation at the Bali talks, adding, "At this stage, we don't want to prejudge the outcome" of talks that are to continue for a projected two years to draw up a treaty to replace the emissions-limiting Kyoto Protocol, which expired in 2012.

The agreement that is to close the Bali conference on Friday, which is seen as a road map for future climate talks, calls on developed countries to make specific cuts in their emissions over the next 13 years.

The European Union favours the proposal, but Australia has said no, saying it wants to set a 2050 target of 60-per-cent reductions instead.

In contrast to Watson, Yvo de Boer, head of the UN Climate Change Secretariat, said early signals over emission reductions were important for investments that need to be made in clean and environmentally friendly technology.

He warned of losing valuable time in the fight against climate change.

"Every week you don't make clear where you want to go is resulting in investments in the wrong direction," he said.

UN Secretary General Ban Ki-moon Ban, who heads to Bali Tuesday, said in a speech in Bangkok that the climate conference "must provide us with a clear road map for tackling climate change."

He added that a breakthrough hinges on the participation of the main polluters among developing countries.

As UN climate talks - which have brought together government delegates, scientists and environmentalists from nearly 190 countries - entered their critical second and final week, environmental groups on Monday warned that delegates had to get their act together if the meeting was to be a success.

"Governments know that if they don't act on climate change, the environmental, social and economic costs will be huge," said Emmy Hafild, executive director of Greenpeace South-East Asia. "When ministers arrive this week, we want to see them hit the ground running."

Environment ministers arriving in Bali have a draft agreement that sets up an emissions goal and the first-ever attempt to recognize national actions to reduce emissions in developing countries, said Angela Anderson with the environmental group, the National Environmental Trust.

"But first they have to resist the urge to put parochial politics ahead of real progress and approve this road map," Anderson said from Nusa Dua, where the two weeks of UN talks were taking place.

The Bali conference has pitted the main polluters from the developed world, the United States and Canada, against the up-and-coming greenhouse gas emitters from Asia, such as China and India.

China, India and other fast-developing Asian nations have argued that the industrialized West is to blame for the bulk of greenhouse gas emissions so the developed economies who should take the lead in commitments to lower their emissions, something the US has refused to do.

Ban, while acknowledging the West's "historical burden," noted it was no excuse for developing countries to do nothing.

"The developing world needs to stop viewing climate change solely as an environmental issue and begin approaching it as a development concern," Ban said.

Recent studies have shown that Asia's teeming populations are likely to be the most seriously affected by global warming through reduced crop production, increasing natural disasters and widespread water shortages.

"Clearly, we ignore this problem at out own peril," Ban said.

The secretary general called on developed nations to come to a "grand bargain" with the developing world by providing better funding for clean energy technologies and easing the transfer of technologies in alternative energies and adaptation techniques.

As calls for cooperation intensified, US environmentalists accused the US delegation of trying to block progress at the Bali conference.

It is trying to deflect from the Bali negotiations by insisting on hosting its own climate talks involving the world's largest economies and polluters, the activists charged, adding that the first meeting in September of the 16 countries that produce 80 per cent of the world's greenhouse gases produced nothing.

"Those meetings have the potential to sap the energy" from the UN talks, said David Doniger of the US environmental group, the Natural Resources Defence Council. "Those are signs of non-cooperation and obstruction."

Karsten Sach, the leader of the German delegation on Bali, said, however, that he believed the US initiative was a positive one. He called them "a very important opportunity" because it intensively involves the United States, which is the only developed country not to ratify the Kyoto Protocol.

Activists have also criticized Canada and Japan. A leaked copy of Canadian government policy exposed a strategy to block the Bali negotiations while Japan appeared to have a similar plan, Greenpeace's Hafild said.

"We don't want to see ministers arriving here with speeches they wrote two weeks ago - they need to roll up their sleeves and do the work that their representatives have failed to finish this week," Hafild said. "This meeting may be in Bali, but this certainly ain't no holiday."