"Let's be frank. Many substantive differences are still remaining," Guterres told reporters as he returned to the COP29 talks.

"We need a major push to get discussions over the finishing line," he said. "Failure is not an option."

Guterres, who also attended COP29 when it opened early last week, said he visited negotiators and felt they were "still largely with their initial positions".

"Now is the moment to move from the initial positions and to find the areas of possible compromise," Guterres said.

He said that a key goal would be seeking an "ambitious" finance goal for poor countries worst hit by climate change.