The spectacular find - at least 230 silver pieces, and possibly twice that number, aged between 2500 and 5000 years old - has been shrouded in secrecy since it was discovered, apparently in the late 1980s.
Found by local treasure hunters in a cave half way up a cliff in western Iran, the hoard fell into the hands of smugglers and part of it is now being dispersed around the world to countries such as Switzerland, Britain, the US and Japan.
But by far the largest chunk of the treasure was seized by the Iranian authorities and is in the possession of two government ministries in Tehran.
The information filtering out of Iran suggests that it is amongst the half-dozen largest ancient treasures ever found anywhere in the world.
"The discovery is extremely important. It is a very major find," said Dr Elizabeth Carter, professor of Near Eastern Archaeology at the University of California at Los Angeles.
"My colleagues and I would urge Unesco to take urgent steps to help recover the smuggled items from the treasure before they are irretrievably scat- tered around the world and lost," said Dr Abbas Alizadeh of the University of Chicago, the only western archaeologist to have seen some of the material in Iranian government hands.
The hoard could easily be worth up to pounds 20m. It consists of between 230 and 500 objects including more than 100 silver bowls, vases and drinking vessels, at least 20 silver animal figurines and statue groups, several silver human masks and numerous other silver items - especially furniture fittings.
There are also some gold items, though relatively few - perhaps because the economies of the ancient Middle East ran on the silver standard and royal treasuries may have consisted largely of silver plate and other silver items.
The animal figurines portray sheep, goats and cattle, and some groups in which lions are shown attacking bulls - a classic Iranian artistic motif.
The masks - perhaps used to adorn statues - probably date from the ancient Akkadian empire of the 23rd century BC and are of extraordinary archaeological importance. There are also a variety of 'ears' possibly made of gold - almost certainly from wooden idols.
The material seems to cover a very wide chronological range, from the 3rd millennium to the 7th or 8th century BC. Some later items - mainly bowls, vases and other vessels - are inscribed in Elamite script with the names of their royal owners. Based in what is now western Iran, Elam was one of the great civilisations of the ancient Middle East.
One possibility is that the hoard was part of the royal treasure of the last known truly independent kings of Elam and that royal officials hid it after the Assyrians sacked the Elamite capital, Susa, in 647 BC. Alternatively the treasure may have belonged to a large temple and was hidden to prevent it being captured by the Assyrians.
Elam first came into existence sometime between 3500 and 2500BC. In around 2000 BC the Elamite dynasty conquered most of southern Mesopotamia. At its zenith, Elam controlled an empire that stretched from what is now the Baghdad area to the entrance to the Persian Gulf.
The discovery of the Elamite treasure could shed new light on the period and give valuable insight into the art of ancient Mesopotamia and Iran - if access and security can be assured.