The cultural body of UN is worried about the building of a giant crematorium at one of the most holiest Hindu sites in Nepal.
Pashupatinath, a temple complex which sprawls over a 2.6 square-kilometre (one square mile) area near Kathmandu on the banks of the Bagmati river, attracts tens of thousands of pilgrims every year from neighbouring India.
Parts of the complex date back to the early fifth century and it was awarded World Heritage Site status in 1979 by UNESCO, putting it on a par with structures such as India's Taj Mahal and the Great Wall of China.
But now UNESCO has pleaded with temple authorities to rethink plans for the construction of a mass electronic crematorium as well as ongoing work to build a road which cuts through the site, fearing irreparable damage.
The organisation's country chief, Axel Plathe, confirmed to AFP that the projects were "a concern for UNESCO" and had asked them to come up with an alternative.
"Construction began without proper authorisation from the competent Nepali authorities as per the established integrated management plan for the property," Plathe added.
In particular, UNESCO is unhappy at the construction of a two-storey building which will house three separate crematoriums.
While defenders of the project say it is more environmentally-friendly than burning bodies in the river, Plathe said no assessment study had been conducted and warned that a giant chimney at the top of the building "will have an adverse visual impact".
Govinda Tandon, the member-secretary of the Pashupatinath Pashupati Area Development Trust, said management was trying to address UNESCO's concerns and wanted to avoid endangering its special status.
"If the temple gets delisted from the World Heritage Site, it will be damaging for us," Tandon told AFP.
"Because there are several government offices involved with the construction works, we are consulting with them."
However he defended the crematorium project, saying it was being built "in order to reduce the environmental pollution because dozens of bodies are cremated on the banks of Bagmati River, using firewood".
An AFP correspondent who visited the site on Tuesday saw dozens of workers laying bricks on the building.
And while construction work on the contentious road through the complex has been halted, several cars could be seen driving across what is currently an unpaved track.
"I use it every day and so do thousands of others because this is convenient for us. I can reach my home in 15 minutes. Otherwise I would have to take a big detour," said 24-year-old student Dipak Rijal.
While UNESCO has not issued an explicit threat to revoke Pashupatinath's heritage status, Tandon said it had been given a deadline of early 2015 for the situation to be resolved.
To date, only two sites have ever lost their world heritage status.
The Arabian Oryx Sanctuary in Oman was removed from the list in 2007 due to the government decision to reduce the size of the protected area by 90 percent.
In 2009, Germany's Dresden Elbe Valley, a 20-kilometre (12 mile) cultural landscape in the city of Dresden was delisted after a four-lane bridge was built in the area.