Negotiators at the United Nations climate talks agreed on a $300bn target to help developing nations adapt to climate change, but many poorer nations have dismissed the agreement as insufficient.

The agreement came on Sunday, a day after the COP29 talks were supposed to end in Baku, the capital of Azerbaijan.

Richer nations agreed to pay at least $300bn a year by 2035 to help poorer countries make their economies more environmentally-friendly, and prepare for natural disasters.

The number is an increase from a previous $100bn pledge, but was still $200bn less than the number called for by a group of 134 developing countries.

A larger target of $1.3 trillion per year was also part of the deal, but most of that would come from private sources.

A delegate from India, Leena Nandan, called the agreement an “illusion”.

“The amount that is proposed to be mobilised is abysmally poor. It’s a paltry sum,” said Nandan. “This document is little more than an optical illusion. This, in our opinion, will not address the enormity of the challenge we all face.”

Hours earlier, delegations from small island states and the least developed nations walked out of negotiations on the funding package, saying their climate finance interests were being ignored.

“We’ve just walked out. We came here to this COP for a fair deal. We feel that we haven’t been heard,” said Cedric Schuster, the Samoan chairman of the Alliance of Small Island States, a coalition of nations threatened by rising seas.

“[The] current deal is unacceptable for us. We need to speak to other developing countries and decide what to do,” Evans Njewa, chair of the Least Developed Countries (LDC) group, said.

When asked if the walkout was a protest, Colombia Environment Minister Susana Mohamed told The Associated Press news agency: “I would call this dissatisfaction, [we are] highly dissatisfied.”

With tensions high, climate activists also heckled United States climate envoy John Podesta as he left the meeting room.

They accused the US of not paying its fair share and having “a legacy of burning up the planet”.

“I know that none of us wants to leave Baku without a good outcome,” COP President Mukhtar Babayev told a late-night session on Saturday after the walk-out, urging all nations to “bridge the remaining divide”.

Later on Saturday, representatives from the European Union, the US and other wealthy countries met directly with those of developing nations in an attempt to work out an agreeement.

Developing countries have accused the rich of trying to get their way – and a smaller financial aid package – via a war of attrition. And small island nations, particularly vulnerable to climate change’s worsening effects, accused the host country presidency of ignoring them throughout the talks.

Before the final deal was announced, Panama’s chief negotiator, Juan Carlos Monterrey Gomez, said he had had enough.

“Every minute that passes, we are going to just keep getting weaker and weaker and weaker. They don’t have that issue. They have massive delegations,” Monterrey Gomez said.

“This is what they always do. They break us at the last minute. You know, they push it and push it and push it until our negotiators leave. Until we’re tired, until we’re delusional from not eating, from not sleeping.”

Developing nations had sought $1.3 trillion to help adapt to droughts, floods, rising seas and extreme heat, pay for losses and damage caused by extreme weather, and transition their energy systems away from planet-warming fossil fuels and towards clean energy.

Wealthy nations are obligated to pay vulnerable countries under an agreement reached at COP talks in Paris in 2015.

Nazanine Moshiri, senior climate and environment analyst at the International Crisis Group, told Al Jazeera that rich countries were being restricted by economic conditions.

“Wealthy nations are constrained by tight domestic budgets, by the Gaza war, by Ukraine and also other conflicts, for example in Sudan, and [other] economic issues,” she said.

“This is at odds with what developing countries are grappling with: the mounting costs of storms, floods and droughts, which are being fuelled by climate change.”