The UN's climate chief urged countries at the COP28 meeting Monday to lift "unnecessary tactical blockades", with 24 hours before the official end of talks in Dubai that are focused on a deal to phase out fossil fuels.

"First, clear the unnecessary tactical blockades out of the way," said Simon Stiell, citing the need to reduce greenhouse gas emissions and support the transition of less developed countries.

"Any strategic landmines that blow it up for one, blow it up for all," he told reporters.

He urged countries to remain ambitious as they seek a way to preserve the goal of checking global warming at no more than 1.5 degrees Celsius above pre-industrial levels.

"I urge negotiators to reject incrementalism. Each step back from the highest ambition will cost countless millions of lives," Stiell said.

"The reality is the highest-ambition outcomes are the only way for all governments to leave Dubai with a win under their belt," he said.

"One thing is for certain: 'I win, you lose' is a recipe for collective failure. Ultimately, it is 8 billion people's security that is at stake."