UN chief Antonio Guterres said a meeting on climate change this year in Scotland is at risk of failure because of mistrust between developed and developing countries, and lack of ambitious goals among some emerging economies.
The UN Cop26 conference in Glasgow in November aims to bring much more ambitious climate action and funds for it from participants around the globe.
Scientists said last month that global warming is dangerously close to being out of control.
"I believe that we are at risk of not having a success in Cop26," Mr Guterres told Reuters on Wednesday.
"There is still a level of mistrust – between north and south, developed and developing countries – that needs to be overcome.
"We are on the verge of the abyss and when you are on the verge of the abyss, you need to be very careful about what the next step is. And the next step is Cop26 in Glasgow."
Mr Guterres and Britain's Prime Minister Boris Johnson will on Monday host a meeting of world leaders during the annual high-level week of the UN General Assembly to build up the chances of success at the climate conference, being held from November 1 to 12.
"My objective and the reason why we are convening a meeting on Monday is exactly to build trust, to allow for everybody to understand that we all need to do more," Mr Guterres said.
"We need the developed countries to do more, namely in relation to the support to developing countries.
"And we need some emerging economies to go an extra mile and be more ambitious in the reduction of air emissions."
Monday's meeting, which will be both online and in person, will be closed to allow for "frank and open discussions" on how to deliver success in Glasgow, a senior UN official said.
Meanwhile, the world remains behind in its battle to cut carbon emissions and the pace of climate change has not been slowed by the global Covid-19 pandemic , the World Meteorological Organisation said on Thursday.
Scientists said last month that unless major action is taken to cut emissions, the average global temperature is likely to hit or pass the level of 1.5°C above pre-industrial times within 20 years.
"Until now, I have not seen enough commitment of developed countries to support developing countries ... and to give a meaningful share of that support to the needs of adaptation," Mr Guterres said.
Developing countries tend to be the most vulnerable to costly climate impacts, and the least resourced to deal with them.
For years, they have been struggling to secure the funds to help them prepare for climate disruptions that rich nations in 2009 pledged to increase to $100 billion a year.
So far, the money that has arrived focused on emissions reduction rather than adaptation. Of the $78.9bn in climate finance transferred by rich countries in 2018, only 21 per cent was spent on adaptation, OECD data shows.
Asked if companies that develop carbon capture technology should have to issue patent waivers so those advances can be shared, Mr Guterres said: "Any development in that area should be a global public good and should be made available to all countries in the world."
But he added: "We have not yet seen results that confirm those technologies will be a key element to solve the problem."
Mr Guterres played down the effect that the increasingly cold relationship between China and the US – the world's two biggest emitters of greenhouse gases – would have on their co-operation on climate change.
"They are a multilateral issue," he said. "So my appeal to both the United States and China is for each of them to do their part."