US banking giants Citigroup, Goldman Sachs, and JPMorgan Chase have become the latest big financiers to rule out funding a major coal port expansion in Queensland, environmentalists say.

Rainforest Action Network, a US environment group, said it had received written commitments from each of the banks to not back the development of the Abbot Point port, which is adjacent to world heritage site the Great Barrier Reef.

The project is being overseen by Indian mining giant Adani, which has government approval to build a new port terminal in order to export coal it will extract in central Queensland, taken to the port via rail.

Several avenues of finance have already been shut off to the $16.5bn project. Deutsche Bank, Royal Bank of Scotland, HSBC and Barclays all ruled out funding the development, before the US banks’ refusal.

Rainforest Action Network said Morgan Stanley had also committed to not investing in the project, although the bank was an adviser to Adani and was helping the company sell part of its stake in Abbot Point in order to provide capital for the development.

Citi and JPMorgan Chase said they would not fund any resources project within a world heritage area, while Goldman Sachs said it ruled out funding a development that “would significantly convert or degrade a critical natural habitat.”

The Adani terminal itself would not sit within the world heritage area and the US banks have not been asked by Adani to study the project and provide funding for it. None of the “big four” Australian banks – ANZ, Westpac, Commonwealth Bank and NAB – have yet ruled out funding the development, despite pressure from climate activists.

However, environmentalists say the stance taken by overseas banks shows that the project is economically and socially toxic.

Conservationists have warned that dredging and extra shipping associated with the port will damage the reef’s coral and fish, while the exported coal will, when burned, result in carbon emissions that will return to haunt the coral ecosystem. A recent government assessment found that climate change was the leading threat to the future of the reef.

Blair Palese, chief executive of climate activist group 350.org, said coal projects such as Adani’s were facing a “perfect storm” of falling coal prices and reluctant investors.

“Adani are quickly running out of options for international finance for this project,” she said. “These banks know a huge amount about investments and they don’t need to look hard to see that this isn’t a good deal. There’s also the reputational damage of being associated with something that will damage the Great Barrier Reef.

“Without a doubt Australia is living in a coal bubble, thinking the world will continue as it always has done. We have a political leader who says coal is good for humanity, which is just sticking your head in the sand. We need to see a rapid transition to renewables, for the good of the climate and also for the good of the Australian economy.”

Aside from the challenge of financing the coal project, Adani has been plagued by allegations of poor employment and environmental practices in India, as well as a court challenge in Australia aimed at stopping its planned Carmichael mine, which would be the largest such development in the country.

However, the company has insisted that there are no issues with the “rigorous and stringent” environmental conditions associated with its coal project.

“They are as robust, if not more so, than any applying to projects that any banks invest in around the world,” Adani said in a statement, adding that Morgan Stanley had confirmed to it that it had not made any judgment of the coal project’s environmental safeguards.

“Morgan Stanley Australia are Adani’s advisers on the potential partial sale of Adani’s existing terminal (T1) at Abbot Point,” Adani said. “Any partial sale of Adani’s current holdings at the port would, far from [being] a withdrawal from the port, in fact be used to deliver the port’s expansion.

“Additionally, Adani has not sought funding for this project from Citibank, Goldman Sachs, or JPMorgan Chase. The premise that institutions who have not been asked to provide funding, have no insight into our projects, and have not studied the details, have declined to or distanced themselves from involvement is rejected.

“Taken together, this demonstrates that this ill-informed campaign mounted by activists with little familiarity with Australia has no basis in fact.”