Poznan, Poland - Any deal to cut emissions of gases blamed for global warming must include all countries or risk failure in the US Senate, a prominent US Democratic senator said Thursday.

Senator John Kerry's comments came during a UN climate conference. They injected a note of caution into the hopes pinned on president- elect Barack Obama, who has pledged to make the United States a leader in fighting climate change.

"The United States will assume its responsibilities - I am confident - for mandatory reductions," Kerry told reporters. "But we will not pass a treaty unless it is a global solution."

He mentioned China and India, two key countries not covered by binding emissions cuts under the UN treaty known as the Kyoto Protocol. China has surpassed the US as the biggest emitter of greenhouse gases by some measures.

"All countries need to be on notice," Kerry said.

Kerry traveled to Poznan, Poland, to attend the final phase of this year's main UN climate meeting, where 189 nations are setting the course for negotiations next year on an emissions-cutting accord due in December 2009.

Kerry, who ran for president in 2004 and is set to chair the US Senate's Foreign Relations Committee, said he would report back to Obama. His meetings Thursday included some with officials from China and Sweden and with UN Secretary General Ban Ki-moon.

Obama, a Democrat, has pledged to cut US emissions to 1990 levels by 2020 and to launch a nationwide system of trading in emissions permits that will force dirty industries to pay for the right to emit pollutants. He has a Democratic majority in both houses of Congress.

Kerry said Congress is committed "to move on mandatory goals as rapidly as possible," with the exact levels to be determined. He suggest that an emissions trading plan, known as cap-and-trade, would be slower to emerge.

Kerry said the world is emitting carbon dioxide, the main global- warming gas, four times faster than in 1990. He pointed to a scenario of rising global temperatures well beyond what scientists have identified as safe.

"That is beyond unacceptable - that is catastrophic in its implications," he said. (dpa)