An official United Nations grouping of 47 of the world’s poorest countries has urged Australia to “honour its international commitments” after the prime minister, Scott Morrison, said the country would not be “throwing money” into a key international climate change fund.

Australia has previously pledged $200m to the Green Climate Fund (GCF), set up through the UN’s climate convention to help developing countries adapt to the impacts of climate change and cut their own greenhouse gas emissions.

But on Monday, in the hours before a major climate report was released, Morrison told radio presenter Alan Jones that Australia would not be “throwing money into some global climate fund”.

One international climate expert said that geopolitically it was “mildly insane” that Australia was backing out of the GCF.

In a statement to Guardian Australia, Ethiopian Gebru Jember Endalew, the chair of the Least Developed Countries (LDC) Group, said: “Funding from wealthy nations such as Australia is key to enabling an effective global response.

“LDCs and other developing countries have made ambitious plans, but these plans cannot be implemented without sufficient tools and resources being mobilised. The Green Climate Fund plays an integral role in delivering these funds and continues to be underresourced.”

The LDC Group represents 47 countries at UN climate negotiations and says its members are “specially vulnerable to climate change but have done the least to cause the problem”. African nations dominate the LDC group, alongside Pacific and East Asian countries Timor-Leste, Kiribati, Vanuatu and Tuvalu.

Endalew said this week’s Intergovernmental Panel on Climate Change report showed “the science is crystal clear that limiting global warming to 1.5C is absolutely vital and that urgent, collective and unprecedented action is required by the international community”.

He added: “Australia and other developed countries are yet to deliver on their collective commitment to mobilise a minimum of US$100bn annually by 2020 to support developing countries. The LDCs will continue to urge Australia to honour its international commitments for the safety and prosperity of present and future generations in Australia, in LDCs, and around the world.”

Australian government ministers have been roundly dismissive of the findings of the IPCC report. Morrison dismissed the report’s relevance for Australia, saying it “deals with the global situation” and claimed, incorrectly, that the “same report” had backed Australia’s policies “only a year ago”. The latest IPCC report was one off and did not assess individual country policies.

Morrison’s dismissive remarks about the GCF contrast with Australia’s previous enthusiastic support for the fund. In 2016, the then foreign minister, Julie Bishop, said Australia’s involvement with the GCF as a co-chair was “instrumental in gaining approval for major climate resilience investments” of US$1.3bn at that time. Chris Tinning, chief economist for development at the Department of Foreign Affairs and Trade, is currently a GCF board member.

A board meeting scheduled for 17 October in Bahrain with board documents showing it will consider $1.16bn in funding proposals. A GCF spokesman said: “We don’t comment on contribution policies of individual countries.”

Dr Bill Hare, the Australian chief executive of respected international climate advisory group Climate Analytics, said the GCF was a “major instrument” that would help lever investments away from fossil fuels.

He said: “In the Pacific, our neighbours are suffering from climate change and the damages they are experiencing are already quite confronting for anyone who cares to notice, and for them the GCF is a major source of resources to help them adapt and to reduce emissions themselves.

“Geopolitically it is, to say the least, mildly insane for Australia at this moment in history in such a sensitive region so crucial to the country’s security, to back out of support for these island countries.”

The former executive director of the UN’s climate convention, Christian Figueres, who led world to the Paris climate agreement, told the ABC on Tuesday that Australians faced a critical moment in history.

“What do you stand for and what do you want history to remember you by,” she said, saying there were clear choices for Australia. “Do you want bushfires raging across the east coast for six months at a time, or do you want a thriving agricultural sector? Do you want the Great Barrier Reef, or the largest aquatic cemetery in the world?”

She said Australia and coal was facing an important moment and that continuing a dependence on coal would deliver “dramatic loss of assets”.

In comments reported in late September, Treasurer Josh Frydenberg indicated Australia had no plans to increase GCF funding, but a Department of Foreign Affairs spokesperson said at the time the government was considering “further contributions”.

On Thursday, a Dfat spokesperson said: “Australia is not planning to provide further funding to the Green Climate Fund (GCF). We will continue to invest in climate change and disaster resilience through our existing development assistance budget, with a focus on the needs of our Pacific partners.”

• This article was amended on 11 October 2018 to include the department’s response.