The website of British auction house Christie's says the beams are from the Great Mosque of Cordoba.

Each is worth as much as $534,000.

They are due to be sold in London on 4 April.

The mosque dates back to the times when the Moors ruled Spain and in its heyday was considered one of the world's most magnificent buildings.

It is classified as a United Nations world heritage site.

The six-metre beams are ornately carved ceiling pieces made from larch wood.

A Spanish law approved in 1985 says specific permission is needed to take any antiquity older than 100 years out of Spain.

Investigation

The Culture Ministry said on Tuesday it has asked Spanish police specialising in artworks, as well as Interpol, to look into how and when the beams were removed from Spain, if they are in fact from the Cordoba mosque and, if so, whether the export was legal.

"...they were always watched over and in good condition. What we don't know is whether some of them disappeared during some move"

Jose Juan Gimenez Gueto,
Archdiocese spokesman

The ministry has contacted Christie's to try to determine how the beams left Spain, and has also been in touch with the British Embassy to ask for help in establishing whether the exportation was illegal, the official said under ground rules barring her name from being disclosed.

The mosque was transformed into a Catholic cathedral in the 13th century after King Ferdinand III, battling to expel the Moors, conquered Cordoba.

Remodelling

The archdiocese of Cordoba, which runs the cathedral - built literally inside the mosque - said on Tuesday it too is trying to ascertain the authenticity of the beams and has hired a team of lawyers in Britain in case it is proven the beams are real and were taken out of Spain illegally.

Archdiocese spokesman Jose Juan Gimenez Gueto said the mosque has undergone remodelling several times over the centuries and some beams were removed and placed in storage or on show.

"But they were always watched over and in good condition. What we don't know is whether some of them disappeared during some move," he said from Cordoba.