Ahead of the meeting, the UN had implored the leaders of the world's richest economies to rescue stalled climate talks in Azerbaijan by boosting funding for developing countries struggling with global warming.

G20 members, who are divided on who should pay, did not make such commitments, saying only that the trillions of dollars needed would come "from all sources."

"The leaders are kicking the can back to Baku," said Mick Sheldrick, co-founder of the advocacy group Global Citizen, referring to the capital of Azerbaijan where the UN climate talks are taking place. 

"This is probably going to make it harder to achieve an agreement," he told AFP.

The risk of an escalation in the war in Ukraine and the prospect of a return of US President-elect Trump's isolationist "America First" policies also dominated the talks in Brazil.

US President Joe Biden is attending the summit, but as a lame duck eclipsed by China's Xi Jinping, who has cast himself as a protector of the international order in the new Trump era.

Xi, who held back-to-back meetings with other leaders, warned the world faced a new period of "turbulence" and said there should be "no escalation of wars, and no fanning of flames."

In a statement, the G20 called for "comprehensive" ceasefires in both Gaza and Lebanon.

The summit was riven with divisions over Ukraine, however.

On Sunday, Biden, who is attempting to ringfence support for Ukraine before Trump's return to power, gave Kyiv the green light to use long-range US missiles to strike deep inside Russian territory.

Biden's move -- a major policy shift by the US -- threatens to escalate a war Trump has vowed to quickly end.

Russia on Monday warned of an "appropriate response" if its territory was hit.

German Chancellor Olaf Scholz said he would not follow Biden's lead with his country's Taurus missiles, but French President Emmanuel Macron praised a "good" move by Biden.

G20 leaders meeting at Rio de Janeiro's Modern Art Museum for a two-day summit tackled an agenda that reflected a shifting global order, trying to shore up multilateral consensus before US President-elect Donald Trump returns to power in January.

Their discussions of trade, climate change and international security will run up against the sharp US policy changes that Trump vows upon taking office, from tariffs to the promise of a negotiated solution to the war in Ukraine.

Leaders at the summit were also able to reach a narrow consensus on the escalating Ukraine war, focused succinctly on "human suffering" and the economic fallout of the conflict.

The leaders' statement also expressed "deep concern about the catastrophic humanitarian situation in the Gaza Strip," and called urgently for more aid and protection for civilians along with a comprehensive ceasefire in Gaza and Lebanon.

After a massive Russian air strike in Ukraine on Sunday, European diplomats had pushed to revisit the previously agreed language on global conflicts, but they ultimately relented.

Russian President Vladimir Putin did not attend the summit, and Moscow was represented by Foreign Minister Sergey Lavrov.

It took marathon negotiations over the weekend for diplomats to finalize the joint statement, with debate over climate policy stretching into the dawn hours of Sunday, according to people involved in the talks.

In their statement, leaders agreed the world needs to reach a deal by the end of the United Nations COP29 climate change summit in Azerbaijan on a new financial goal for how much money rich nations must provide to poorer developing nations.

COP29 officials had called on the G20 leaders for a strong signal to help breach the impasse on climate finance. While the joint statement said nations need to resolve the issue, they did not indicate what should be the solution at the UN summit set to end on Friday.

As host of this year's G20 meetings, Brazil expanded the group's focus on extreme poverty and hunger, while introducing debate on cooperation to fairly tax the world's wealthiest - topics also highlighted in the leaders' joint statement.