A plan by US President George W Bush for countries to set their own targets for reducing greenhouse gas emissions has drawn considerable criticism.
Mr Bush said the US was taking the climate change issue seriously
Some delegates at a meeting of the world's top 16 polluters saw Mr Bush's comments as a US reluctance to commit to binding action on global warming.
Officials at the Washington forum said legally-set international targets were the only way to tackle climate change.
Mr Bush stressed that combating climate change should not damage the economy.
And he again hinted that the US would not commit itself to mandatory CO2 cuts.
"Each nation must decide for itself the right mix of tools and technology to achieve results that are measurable and environmentally effective," Mr Bush told delegates in Washington.
But his comments did not go down well with a number of the ministers, diplomats and officials attending the US-sponsored forum on energy security and climate change.
South African Environment Minister Marthinus van Schalkwyk said in a statement: "What [the US] placed on the table at this meeting is a first step, but is simply not enough.
"We think that the US needs to go back to the drawing board."
The British climate envoy, John Ashton, said the US seemed isolated on the issue of fighting climate change.
"I think that the argument that we can do this through voluntary approaches is now pretty much discredited internationally," he told the Reuters news agency.
The BBC's environment correspondent Matt McGrath, in Washington, said Mr Bush's plan did not sit well with the majority of delegates.
The plan exposed serious differences over the best way forward on climate change, he added.
Shortly after taking office in 2001 Mr Bush said he would not ask Congress to ratify the Kyoto Protocol on cutting emissions, and has consistently opposed mandatory cuts.
Instead the president has championed voluntary approaches - echoed by China and India.
Mr Bush urged delegates on Friday to set a joint long-term goal for reducing the CO2 emissions that were causing the climate to heat up.
"By setting this goal, we acknowledge there is a problem. And by setting this goal, we commit ourselves to doing something about it," Mr Bush said.
Activists want the US to take the lead in solving the climate crisis
He told delegates his Washington forum would work within the framework of UN-led negotiations to craft a successor to Kyoto, due to begin in December in Bali, Indonesia.
But he stressed that it was possible to cut emissions without harming economies.
"We must do it in a way that does not undermine economic growth or prevent nations from delivering greater prosperity for their people," he said.
Humberto Rosa, a Portuguese minister representing the EU, welcomed the "firm and strong message", which he said was in "sharp contrast" to previous US attitudes.
Teams from Australia, Brazil, Britain, Canada, the EU, France, Germany, Japan, India, Indonesia, Italy, Mexico, South Africa, South Korea, Russia and the US took part in the Washington forum.