UNESCO has condemned a decision to allow the dumping of dredge waste in Great Barrier Reef waters.
It has recommended the Australian marine park be considered for inclusion on the World Heritage in Danger list.
The decision in January to allow three million cubic metres of dredge waste to be disposed of in park waters followed a decision by the government to give the green light to a major coal port expansion for India's Adani Group on the reef coast in December.
Conservationists warn it could hasten the demise of the reef, which is already considered to be in "poor" health, with dredging smothering corals and seagrasses.
They say the actions expose them to poisons and elevated levels of nutrients.
In its first comments on the issue, the United Nations Educational, Scientific, and Cultural Organisation "noted with concern" and "regrets" the move.
It said it "was approved despite an indication that less-impacting disposal alternatives may exist".
It asked the government to provide a new report to the World Heritage Committee proving that dumping was the least damaging option and would not hurt the reef's value.
UNESCO expressed concern "regarding serious decline in the condition of the Great Barrier Reef, including in coral recruitment and reef-building across extensive parts of the property".
It said: "A business-as-usual approach to managing the property is not an option."
Given the reef's long-term deterioration, it recommended the World Heritage Committee consider putting it on its in-danger list in 2015 "in the absence of substantial progress on key issues".
WWF Australia spokesman Richard Leck said the government needed to act quickly to prevent the embarrassment of the reef being listed as in danger.
"UNESCO'S concern is shared by thousands of Australians and hundreds of leading scientists and we call on the federal government to ban dumping of dredge spoil in the Great Barrier Reef World Heritage Area prior to the World Heritage Committee meeting in June," he said.
The government in February insisted it had made "substantial" progress on UNESCO benchmarks for protection of the reef in a report aimed at staving off a world heritage downgrade.
Environment Minister Greg Hunt said it "demonstrates unequivocally the government's commitment to better managing and protecting this natural wonder".
According to the report, Australia was taking steps to bolster the reef's resilience to the major threats of extreme weather events and climate change, which it said "cannot be managed directly".
Working to reduce outbreaks of the coral-feeding crown-of-thorns starfish was a priority, as was tackling nutrient and sediment run-off from land-clearing and agriculture, the report said
On port development, it said no projects "have been approved outside the existing and long-established major port areas within or adjoining" the reef.