The controversial decision to green light a £100m golf resort close to the Giant's Causeway undermines the international treaty governing World Heritage Sites, conservationists claim.
Tim Badman, director of the World Heritage Programme of international conservation body IUCN, says concerns are being raised over how seriously the World Heritage recognition of the Giant's Causeway is being taken in Northern Ireland.
The National Trust commented that it was extremely concerned about anything that could put World Heritage status in jeopardy.
Earlier this week a High Court judge dismissed the National Trust's judicial review of the decision to grant planning permission for the Bushmills Dunes project, which lies within the buffer zone of Northern Ireland's only World Heritage Site. The developers plan to build a championship links golf course, five-star 120-bedroom hotel and spa and 75 villas at Runkerry.
Mr Badman said the timing of the decision was very unfortunate as a representative of IUCN had travelled to the Giant's Causeway last week to investigate.
Last year, Environment Minister Alex Attwood announced he would grant planning permission for the Bushmills Dunes resort despite his own Northern Ireland Environment Agency department recommending refusal.
Unesco then called for a halt to the development until a mission could be undertaken.
IUCN is currently preparing a report on the mission but this cannot be presented to Unesco's World Heritage Committee until it meets in June.
This week the DoE said the resort could now go ahead and the developers said they would be embarking on site preparation work immediately.
Mr Badman said: "We had somebody on the site looking at this issue between Wednesday and Friday of last week so the timing is very unfortunate – to be in the process of trying to give advice following a request from Unesco and to have the judgment at almost the same time negates the consideration of the World Heritage values of the Giant's Causeway."
The DoE said the World Heritage status of the site has been taken into consideration.
A statement issued said: "In arriving at a decision to grant permission, all the material considerations were thoroughly scrutinised including any impact on the World Heritage Site.
"The court did not uphold any of the grounds of legal challenge."
Heather Thompson, regional director at the National Trust, said: "We look forward to receiving the Unesco report following their recent visit to the site in February."