The EU remains hopeful of securing a deal to rescue the Kyoto protocol as climate change talks dragged on into Saturday evening in Qatar, where 195 countries have gathered to thrash out a new deal on greenhouse gas emissions.

Most of the key issues have been resolved, including a last-minute legal hitch affecting Poland. However, one sticking point emerged when Russia and Ukraine tried late in the day to reopen negotiations on the agreed text.

Ministers were trying frantically to resolve the problem, which centred on so-called "hot air" – carbon credits issued under the Kyoto protocol to Eastern Bloc countries, based on their 1990 emissions. As their emissions crashed along with their inefficient industry after the fall of communism, these countries now have an excess of credits they want to be allowed to keep and sell. Other countries argue this would remove the "environmental integrity" of any new agreement.

By 6pm Saturday – 24 hours after the deadline, and after a night spent locked in huddles of small groups of ministers – talks had still not reconvened for what should have been the penultimate meeting. Officials said it was impossible to predict when they might conclude.

Other key issues are yet to be fully resolved, as the fortnight-long talks entered extra time. These included financial assistance for poor countries suffering the effects of climate change, and how to structure a proposed new global climate change agreement that would be signed in 2015 and come into force in 2020.

But the marathon session left many delegates hopeful of rescuing a deal, amid the frustration and confusion of Friday night. "We have worked without a break and people realise we need to go home with something," said one delegate.

Ed Davey, the UK energy and climate secretary, worked through the night, meeting with ministers from developed and developing countries in an attempt to secure a deal.

Rumours and counter-rumours were flying throughout the day as ministers met in small groups to hammer out compromises. Some meetings were fractious, with delegates conscious of the need to avoid a breakdown. Such an outcome would be disastrous for the image of the summit with the eyes of the world upon the 195 governments meeting in Doha.

Delegates were close to reaching an agreement to close down parallel negotiations set up after the protocol came into force in 2005, at the behest of the US, which has always rejected Kyoto. Closing that strand would enable unified negotiations to begin work on a proposed new global climate change agreement, which would require emissions cuts from both developed and developing countries. It would be signed in 2015 to come into force from 2020.

Progress on other issues was still unclear late on Saturday afternoon, including whether and how poor countries would be compensated for the damage done to them by climate change – the so-called "loss and damage" clause.

Developing countries wanted a new institution and framework to deal with this, but the US was opposed such a measure. However, a compromise was said to be possible that would allow the US to agree a new mechanism that fell short of the developing countries' strongest demands but would ensure the end results – of compensation and assistance to poor nations – were achieved.