Fierce bargaining at UN climate talks in Azerbaijan dragged into Saturday after a $250 billion a year offer from rich nations was flatly refused by developing countries hardest hit by Earth's rapid warming.

Negotiations at Cop29 in Baku, Azerbaijan were scheduled to finish on Friday evening but a final deal on climate finance remains elusive.

The European Union, United States and other wealthy countries at the COP29 climate summit have agreed to raise their offer of a global finance target to $300 billion per year by 2035, sources told Reuters on Saturday.

COPs have been getting progressively longer; the excellent team at Carbon Brief extrapolated the trend line, which suggests COP29 will end in the small hours of Sunday morning. Even that may be optimistic.