Spain's Altamira cave, dubbed the "Sistine Chapel" of Paleolithic art because of the paintings of animals on its ceiling, will no longer reopen to the public as planned at the end of the year.
The cave located some 30 kilometres (19 miles) west of the northern city of Santander has been closed since 2002 because the breath and body heat from visitors threatened the fragile natural pigments used in the cave art.
But in June the foundation which manages the the cave announced it would reopen the site to the public at the end of 2010 once a panel of experts determined how many people could safely be allowed to visit.
Now officials have reversed course. Spain's culture ministry said in a statement late on Thursday that "today it is not advisable to change the conditions for access to the cave or propose public visits."
The ministry said a "multidisciplinary international group" of conservation experts would be set up that will determine what impact human presence has on the rock art in order to decide if visits to the cave should be allowed.
The group will deliver its findings within a "maximum period of two years", the ministry added.
The lifelike drawings on the cave's ceiling of deer, wild boar, bison and horses beautifully rendered in shades of red, yellow, black and brown that are estimated to be at least 14,000 years old were discovered in 1879.
Tens of thousands of people visited the cave over the next century until it was closed to the public for the first time in 1977.
It was reopened in 1982 but with restrictions on the number of people who could visit it and remained open until September 2002.
Some 2.5 million people have visited a replica of the cave located in the northern town of Santillana del Mar since it opened eight years ago.
The Altamira cave was declared a World Heritage Site by UNESCO in 1985.