Japan led the way by promising to stump up a whopping 1.75 trillion yen (19.5 billion dollars), including 1.3 trillion in public funds, for developing nations on climate change if a comprehensive deal is reached at Copenhagen.

It was also one of five countries -- along with Australia, Britain, France, Norway and the United States -- that said they would set up a fund to fight the loss of forests, a leading source of the rising temperatures that scientists warn will cause droughts, plagues and storms if unchecked.

"Japan as a country takes very seriously its responsibility in the international community," Environment Minister Sakihito Ozawa said as he announced the biggest financial offer yet for climate change.

Europe has already said it would give 7.2 billion euros (10.6 billion dollars) towards an envisioned fund worth 30 billion dollars to help developing nations tackle climate change over the three years from 2010-2012.

The United States has yet to announce a contribution, although the White House has said it will offer a "fair share."

The package is viewed in Copenhagen as a sign of goodwill on longer-term finance, which is a core part of an overall deal for rolling back climate change.

In a joint statement, the six governments also said they would collectively dedicate 3.5 billion dollars from 2010 to 2012 in what they hoped would be just the starting point for a deforestation fund by wealthy nations.

The announcements were intended to provide fresh momentum as delegates feared an overwhelming amount of work remained to seal a deal ahead of the summit's finale on Friday when around 120 world leaders are due in Denmark.

After a day marked by finger-pointing, Britain's climate minister Ed Miliband feared a deal could slip away.

"People can kill this process, kill the agreement with process argument," Miliband said, warning the talks were at a "very dangerous point."

Developing countries, led by China, accused host Denmark of a lack of transparency by suggesting language for the agreement without full consultation by all sides on the 194-nation summit.

"There's a group of countries who think they are better than us in the South, in the Third World," said Venezuelan President Hugo Chavez, who railed against "the imperial dictatorship" of the West.

The anti-capitalist theme was picked up on by Robert Mugabe, Zimbabwe's veteran president who is the target of Western sanctions over alleged human rights abuses.

"When these capitalist gods of carbon burp and belch their dangerous emissions, it's we, the lesser mortals of the developing sphere who gasp and sink and eventually die."

The leaders of Bangladesh and Nepal pleaded for the summit to be ambitious, warning they faced some of global warming's worst ravages.

"Bangladesh's greenhouse gas contribution is negligible, but it is one of its worst victims," Prime Minister Sheikh Hasina said.

Tensions also flared outside, where police used clubs and tear gas to stop some 2,500 activists who tried to march on the tightly guarded Bella Center.

Police said they rounded up some 260 demonstrators, some of whom clashed again with the guards of their makeshift jail in a former beer warehouse.

Activists were outraged after the UN Framework Convention on Climate Change (UNFCCC), which is running the 12-day conference, turned away thousands who were registered, saying the building was at maximum capacity.

The summit climaxes Friday when the leaders including US President Barack Obama try to lay out a strategy to deal with climate change after the end of 2012, when obligations run out under the landmark Kyoto Protocol.

Obama, due here Friday, has offered to cut US carbon emissions by 17 percent by 2020 over a 2005 benchmark, a figure that aligns with legislation put before Congress but is well below pledges by the European Union and Japan.

"The president is hopeful that his presence can help," said White House spokesman Robert Gibbs, as US lawmakers tried to dash through business and catch a plane to the Danish capital.

In Paris, French President Nicolas Sarkozy met with African leaders and appealed for help for the Congo basin, home to the world's second biggest forest, warning they "cannot on their own maintain a forest that is the heritage of humanity."

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