Delegates at the world trade talks in Mexico are making a final effort to reach agreement on contentious issues.
Protesters have kept up the pressure
Their conference is due to end on Sunday evening but after four days of talks they remain deeply divided on agricultural subsidies and rules on how countries should treat foreign investors
A senior member of the United States team, Josette Shiner, described Sunday's session as critical and correspondents say the mood is sombre.
The main disagreement is over subsidies paid to farmers in rich nations, but developing countries are also upset by proposals to negotiate new rules on foreign investment.
No country is entirely happy with the latest draft circulated about 24-hours ago. A top European Union official said it crossed several red lines.
It calls for an end to export subsidies on farm products of special interest to developing countries, designed to tackle the most harmful impact of subsidised exports from the United States and Europe.
But it falls short of the sweeping elimination of subsidies that a new bloc of developing nations - known as the G21 and including Brazil, China and India - has pressed for.
Josette Shiner said: "If all parties are unhappy, we've probably got the imbalances about right, but we have to remember why we're here: we have a once in a generation chance to bring down barriers that end up hurting the consumers and the people in all our nations."
The BBC's Andrew Walker, in Cancun, says many developing countries are much less relaxed about what is currently on the table.
The Indian commerce minister, Arun Jaitley, said that one aspect of the agriculture proposals provides special treatment for the rich countries, which he described as utterly incomprehensible.
Malaysian trade minister Rafidah Aziz rejects proposals for negotiations which might lead to rules on how countries treat foreign investors, and describes her position as non-negotiable.
There are many hours of tough negotiations ahead, our correspondent adds.
Against the chorus of criticism from across the developing world, the EU too is complaining. It says it is getting a rough deal on domestic farm subsidies.
The EU and US say poorer countries must agree to broader legal and commercial reforms in return for any concessions on farming.
But if no compromise is achieved, the prospects for negotiating a new global trade deal by the end of next year will be even more uncertain, our correspondent says.
About 2,000 demonstrators armed with stones and shields and chanting "WTO murders" marched through Cancun on Saturday to denounce the talks - but were kept away from the conference centre.
There is a whole series of issues at stake besides removing distortions in global agricultural trade, including contentious ones dealing with foreign investment and competition policy.
But the focus of this conference has been very much on the subsidies paid to European and American farmers and the impact this has on producers in the developing world and also on access to markets.