World climate talks late Thursday inched towards common ground that would bring China, the United States and Europe into a deal on tackling global warming.
Facing escalating demands to cut a deal by the close of the talks late Friday, the United States said it supported a European proposal for a "roadmap" towards a new pact on carbon emissions.
But key details on this apparent shift remained blank and true to the gruelling traditions of climate conferences, wrangling was likely to continue into the early hours of Saturday.
Chris Huhne, Britain's minister for energy and climate change, declared the United States was having to give ground in the face of a united call from two-thirds of the world's nations.
"I think the US is reflecting the pressure that's been brought to bear and is continuing to be brought to bear on many of the other members here who have yet to agree," he said.
"We are making progress, we're not there yet, we are making progress."
Delegates also saw movement on designing a "Green Climate Fund" that by 2020 would catalyse up to 100 billion dollars a year in aid to poor countries exposed to worsening drought, flood, storms and rising seas.
The 12-day talks are the annual get-together of the UN Framework Convention on Climate Change (UNFCCC), a child of the 1992 Rio Summit.
But the main source of climate-altering greenhouse gases is cheap and plentiful fossil fuels, which are vital for the world's economy.
As a result, the forum is struggling to make headway, even as scientists say only a few years are left before emissions must peak and then go swiftly into reverse.
Chances of a deal hinge on the Kyoto Protocol, the UNFCCC's cornerstone achievement.
Kyoto is the only treaty that stipulates legally-binding curbs on greenhouse-gas emissions, although critics say its format is deeply flawed.
These constraints only apply to rich countries that have ratified it -- thus it leaves out the United States, which abandoned the Protocol in 2001 -- nor do they concern developing countries, on the grounds of their relative poverty.
For these countries Kyoto has iconic value, representing rich countries' historic responsibility for climate change.
But without fresh pledges, the treaty could be left in limbo at the end of 2012.
Canada, Russia and Japan have refused to renew their Kyoto vows beyond this date, given that emerging giants and the United States, accounting for the vast majority of greenhouse-gas emissions, have no legal binds.
The European Union has promised to endorse a second round of pledges, but only if big emitters, led by China and the United States, back a "roadmap" leading to a new, legally binding treaty for everyone.
US chief delegate Todd Stern noted that the United States had previously called for a pact that brought all emitters into the same fold.
But in a shift in tone, he backed the concept of a roadmap, but left unsaid whether this should be legally binding as Europe demands.
"If we get the kind of roadmap that countries have called for -- the EU has called for, that the US supports -- for preparing for and negotiating a future regime... we are strongly committed to a promptly starting process to move forward on that," he said at a press conference.
"Whether it ends up being legally binding or not, we don't know yet," he added.
Stern said, though, the best gains came from pragmatic advances, such as the Green Climate Fund, that were launched at the stormy 2009 Copenhagen Summit and endorsed last year in Cancun, Mexico.
Several European ministers stood alongside counterparts from developing countries to emphasise what Huhne said was overwhelming support for the roadmap.
"We calculate that 120 of the 193 countries represented here want what we are standing up for today," he said.
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