The leaders of the world's 20 richest economies were under pressure during their summit in Brazil to break the impasse over climate finance at the deadlocked COP29 talks in Azerbaijan.

A statement issued by G20 leaders in Rio de Janiero overnight reiterated support for a deal to be reached in Baku, where the first week of negotiations ended in bitter stalemate.

"We needed to see a strong signal from the G20, and we got that on finance," said Mohamed Adow, a Kenyan climate activist and founder of the Power Shift Africa group.

Jasper Inventor, from Greenpeace, described the support for a finance deal as "a positive signal".

"This momentum must now be translated into concrete outcomes in Baku," he said.

Rich nations are being urged to significantly raise their pledge of $100 billion a year in finance for poorer countries to take action against climate change.

But efforts to finalise the deal in Baku have been glacial, with rows over how much the deal should entail, who should pay it, and what types of finance should be included.

The chair of the G77 + China, a grouping of developing nations, told AFP that the Rio statement was a "good building block" for the climate talks as G20 leaders acknowledged that the needs were in the "trillions" of dollars.

However, Adonia Ayebare, the group's Ugandan chairman, said that the G77 was "not comfortable" with vague wording saying the money should come from "all sources".

"We have been insisting that this has to be from public sources. Grants, not loans," Ayebare said.

Harjeet Singh, an activist from India, said the G20 "displayed a stark failure in leadership".

"Their rehashed rhetoric offers no solace for the fraught COP29 negotiations, where we continue to see a deadlock on climate finance," he said.

The statement did not explicitly repeat a pledge made last year at COP28 to transition the world away from fossil fuels, a flashpoint issue that has caused tensions in Baku.

G20 leaders made reference to phasing out "inefficient fossil fuel subsidies" but the key language enshrined to much fanfare in the commitment made in late 2023 was absent.

"Silence on the new climate finance goal and mutism on fossil fuel phase out are unacceptable coming from the biggest economies and emitters," said Rebecca Thissen from the Climate Action Network.