US President Barack Obama (R) speaks during a meeting of the US-European Union Summit as Prime Minister of Sweden Fredrik Reinfeldt looks on, in the Cabinet Room at the White House in Washington November 3, 2009. [Agencies]

WASHINGTON: US President Barack Obama and European Union leaders pledged on Tuesday to redouble efforts for a deal on climate change at a summit in Copenhagen, but gave no details of how to reach that ambitious goal.

"We discussed climate change extensively and all of us agreed that it was imperative for us to redouble our efforts in the weeks between now and the Copenhagen meeting to ensure that we create a framework for progress," Obama told reporters.

The UN conference to fight climate change will be held in Copenhagen from December 7 to 18, pitting emerging economic powerhouses China and India against Western industrial nations in the drive to reduce greenhouse gas emissions.

Obama spoke after a White House meeting with European Commission President Jose Manuel Barroso, EU Foreign Affairs chief Javier Solana and Swedish Prime Minister Fredrik Reinfeldt, whose country currently holds the EU's collective presidency.

The Europeans sounded optimistic a deal was within reach.

Barroso earlier told reporters not to expect "a full-fledged binding treaty - Kyoto type - by Copenhagen."

But German Chancellor Angela Merkel told US lawmakers after meeting with Obama earlier on Tuesday that a deal was urgent and there was "no time to lose."

Merkel, making the first address by a German leader to a joint session of the US Congress since Konrad Adenauer in 1957, was much more specific in what a deal would require.

"We need an agreement on one objective - global warming must not exceed 2 degrees Celsius (3.6 F)," she said. "To achieve this, we need the readiness of all countries to accept internationally binding obligations," she said.

In a declaration issued after the US-EU summit, the leaders said they had agreed "to promote an ambitious and comprehensive international climate change agreement in Copenhagen."

"Together, we will work towards an agreement that will set the world on a path of low-carbon growth and development, aspires to a global goal of a 50 percent reduction of global emissions by 2050, and reflects the respective mid-term mitigation efforts of all major economies, both developed and emerging," the statement said.

The leaders also said they would "work to mobilize" significant financial resources to support climate efforts by developing countries and strengthen efforts to develop strong carbon markets.

Work toward a new deal ran into obstacles in the US Senate and at UN negotiations that began on Monday in Barcelona, Spain, the last session before Copenhagen.

In Barcelona, African nations staged a daylong boycott of part of the 175-nation UN climate talks to demand far deeper 2020 cuts in greenhouse gas emissions by rich countries.

African nations want the rich to cut by at least 40 percent below 1990 levels by 2020, saying their people are hit the most by disruptions to water and food supplies.

"People in Africa are suffering now, people are dying now, when the developed countries are not willing to express ... ambitious reductions," said Kemal Djemouai, chair of the African group.

The African nations agreed to lift the boycott on Tuesday after winning promises that industrialized nations would spend more time in Barcelona discussing cuts in emissions. Disputes over emissions reductions are a main stumbling block to a Copenhagen deal.

In Washington, Senate Democrats on a key committee began a debate on reducing US carbon dioxide pollution despite a boycott by Republicans who want to delay climate change legislation.

Senate Environment and Public Works Committee Chairman Barbara Boxer told reporters at the end of the first work session that she sensed a "fundamental shift" in the debate because of a letter she received from the US Chamber of Commerce.

The business group, which has long opposed climate change legislation, said it wanted to engage in a "new conversation" on the issue. But it did not embrace the central approach of the legislation before Boxer's committee: government mandating carbon dioxide emission reductions on industry.

Full US legislation is unlikely before Copenhagen.

The US bill seeks to cut emissions of greenhouse gases by 20 percent by 2020, from 2005 levels - a cut of about 7 percent below 1990 levels used as the benchmark for the Kyoto Protocol.

In London, UN Secretary-General Ban Ki-moon said a Copenhagen deal in December would be "a very important milestone." But he said it would not be a detailed legal text, reflecting a global scaling back of ambition for the meeting.