In a late-night session, negotiating groups reported they had settled some disputed wording and clauses, but other knotty issues remained to be sorted out.
One issue, related to pledges by industrial and developing countries to rein in emissions of heat-trapping gases, appeared deadlocked.
Despite the reported progress, the EU's top climate official, Connie Hedegaard, said countries were withholding approval on all issues until everything is ready.
Observers from the European Union criticised the biggest players in the talks, the United States, Japan, China and others, for refusing to budge on legal limits to emissions and blocking attempts to forge a framework that could lead to sharp cuts in carbon gases.
"It is really a pity that the Kyoto parties and the convention parties cannot come together, and the ping pong game between the US and China that has damaged Copenhagen is likely to damage again Cancun," EU delegation head Joseph Mathias Leinen said on Friday.
"Europe is seriously disappointed" in the current round of negotiations he said.
Whatever the outcome, delegates and activists say some progress has been made on secondary issues, which they hope will continue to build a framework for further agreements in later rounds of negotiations.
"The real challenge now is to find a compromise text that will allow countries to take forward a result out of here, that's most important. But not just any result, it has to be a result that actually is worth the paper it's written on," Antonio Will of Oxfarm said on Friday.
A key issue of contention was whether to make the post-Copenhagen national emissions pledges legally binding, and in what kind of document.
The United States rejected Kyoto, the only industrialised country to do so, because it didn't require fast-growing economies such as China and India to limit their emissions.
Developing countries attach huge importance to Kyoto as their only legal weapon against the wealthy countries, whom they blame for creating the global warming problem by dumping greenhouse gases into the air for 200 years.
Activists staged numerous events around the summit on Friday trying to take their message to delegates gathered within the summit venue to hammer out compromise proposals.
Greenpeace activists staged a "lifeline" to delegates featuring a giant life saver ring, representing a symbolic attempt to rescue the talks from gridlock.
They spelled out the message "hope" with their bodies on a beach in Cancun's hotel district.
Oxfam built a sand sculpture representing indigenous peoples as a way to highlight their commitment to the rights of the poor and forest dwellers.
Anti-meat activists stripped down to their skivvies in front of the summit venue, holding signs decrying the cattle and ranching industries, saying such activities are a major cause of global warming.
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