The islands are about 41 miles west of Benbecula

St Kilda, off the Western Isles, already had World Heritage status for its bird colonies.

But now the United Nations has extended that to include the seas surrounding the islands.

The UN's cultural body, Unesco, was considering St Kilda's status at a meeting in China and announced the decision on Thursday.

New evidence

The bird colonies on the islands have been protected since they were given the prestigious World Heritage Site status in 1986.

The archipelago's owners, the National Trust for Scotland, have long wanted an extension to that protection to include its marine environment and cultural landscape.

A research project exploring the underwater environment four years ago provided new evidence about the seas surrounding one of the most isolated outposts of the British Isles.

However, a bid to include recognition of the islands' lost crofting community was deferred for more information.

ST KILDA 41 miles west of Benbecula Evacuated in 1930 Left to the National Trust for Scotland in 1957 A major seabird breeding station Visiting St Kilda

Robin Pellew, chief executive of the National Trust for Scotland, said: "Whilst we are disappointed that the decision relating to the cultural aspects of the site has been deferred until next year, the extension to include the marine environment is an important decision to help protect the natural environment surrounding the islands.

"The shores and sea-bed around St Kilda are more or less unaffected by human intervention making it unique in the world."

The bid for cultural status will be considered at a world heritage committee meeting in South Africa in June 2005.

A plan to put remote controlled cameras on St Kilda was turned down in October last year by the Western Isles Council.

The cameras would have allowed visitors to the National Seabird Centre at North Berwick to view live pictures of the bird colonies on the islands.