Wealthy nations have come under attack from developing countries over proposed financial commitments designed to help them deal with the effects of global warming.

The row, which came at the close of the first week of the crunch Paris climate talks, was over the wording of a proposal in the draft text of a potential agreement released on Friday, which became the subject of long negotiations into the early hours of Saturday morning.

The world’s least developed countries face the greatest threat from climate change as they lack the technology to cut greenhouse gas emissions and their infrastructure is too fragile to cope with extreme weather. Under the proposed wording, developing countries with rapidly growing economies, such as China, would be included alongside established developed nations in being regarded as potential donors to poorer nations.

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Rich countries argue that the wording merely reflects current reality, as at least eight governments classed as developing have already made “climate finance” contributions that will aid those poorer than them. China pledged $3bn (£2bn) to the Green Climate Fund in September, and has made further pledges to help Africa.

But some developing countries see the attempt to bracket them with the rich as a threat. They think it could be used in the future to force them to become donors alongside countries such as the US and the EU.

Susheel Kumar, a senior environment official in India, said: “The language is not in line with the framework convention. It is trying to redraft the convention.”

He was referring to the original 1992 UN Framework Convention on Climate Change, and the subsequent Kyoto protocol, which enshrined the doctrine of “common but differentiated responsibility”, by which rich and poor were seen to have different roles. The concept has been controversial, because in the past it has been taken to absolve developing countries – even competitors such as China – from the need to cut emissions, enraging conservatives in the US and elsewhere.

Todd Stern, the US special envoy for climate change, said: “There are developing countries moving to being donors. This recognises that there are more advanced developing countries.”

He insisted that no developing country would be obliged to provide financial assistance to those worse off and that providing financial assistance would be entirely voluntary. “Some people have over-reacted to this or read it incorrectly,” he said.

The row may be resolved if appropriate wording can be agreed, but it will not be the end of wranglings on finance. The issue of how to provide adequate financial assistance to the poor is likely to be one of the biggest at the talks.

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The two-week Paris conference aims to forge a new global agreement, to come into force from 2020, when current commitments on greenhouse gas limits run out. It is seen as a make-or-break meeting because if the negotiations fail the world will be left without a means to take effective collective action on global warming.

Delegates are facing another week of tough negotiations, with late nights the norm since world leaders opened the conference on Monday. Sunday was supposed to be a day free of official negotiations, but meetings among countries will continue all day.

The latest draft text is 38 pages long, a version that contains many “bridging options” – inserted to reflect areas of remaining disagreement. Countries are being asked to pick from these options, some of which are radically different to each other but others simply show a small change of wording, and eliminate as many of them as possible.

This is supposed to be accomplished by noon on Saturday but as with many deadlines at the conference, the timing may slip – and at that point the French hosts want to receive a streamlined version of the text. They will then re-examine it and possibly redraft or suggest changes, ready to give back to “facilitators” or to the government ministers who will arrive next week.

While some of the discussions will be technical, over legal wording, the ministers will also be charged with making political decisions – such as on finance, and whether to include a long-term goal on limiting global temperature rises.