"A successful outcome at COP29 is still within reach, but it will require leadership and compromise, namely from the G20 countries," Guterres, who will attend the summit of the world's biggest economies starting Monday, told a press conference in Rio.

The annual UN talks in Baku are deadlocked at the midway point, with nations no closer to agreeing a $1 trillion deal for climate investments in developing nations after a week of negotiations.

The talks are stuck over the final figure, the type of financing, and who should pay, with Western countries wanting China and wealthy Gulf states to join the list of donors.

All eyes have turned to Rio in the hope of a breakthrough.

"The spotlight is naturally on the G20. They account for 80 percent of global emissions," Guterres said, calling on the group to "lead by example."