By Peter Fray in London and Alexa Moses

Several museums in Europe and the United States have issued a landmark declaration opposing the wholesale repatriation of cultural artefacts seized during imperial rule or by means now considered unethical.

The museums say the universal value of collections of archaeological, artistic and ethnic objects in promoting culture outweighs the desire by individual countries or racial groups for their return.

The declaration is the most significant attempt by the world's leading museums to protect treasures, often seized during colonial rule, from governments or descendants of original owners.

Disputed high-profile treasures include the Elgin Marbles and the Benin bronzes in the British Museum and several thousand Egyptian works in the Louvre. The declaration on the "value of universal museums" may harm Australian Aboriginal campaigns for the return of artefacts and human remains from Europe.

It shows how difficult it will be for Aboriginal campaigners and Australian museums to persuade many European institutions to return pieces from their collections. Signatories include the Louvre in Paris, the Hermitage in St Petersburg, the Prado, Madrid, the Metropolitan, Guggenheim, Whitney and Museum of Modern Art in New York, the Rijksmuseum, Amsterdam, and the State Museums, Berlin.

The British Museum, which has a collection of Aboriginal remains, did not sign the declaration, but said its director, Neil MacGregor, supported its intent. Yesterday it was releasing the declaration to British-based media on request. "We don't believe in breaking up collections," said a spokesman, Andrew Hamilton.

The declaration described repatriation as "a disservice to all visitors", though it said requests for specific objects would be judged on an individual basis. "We should acknowledge that museums serve not just the citizens of one nation but the people of every nation," it said.

"We should recognise that objects acquired in earlier times must be viewed in the light of different sensitivities and values, reflective of that era."

Mr Hamilton said the British Museum was a place where "you can come and see the entire history of mankind in one place".

The British Government will soon receive a report on the repatriation of human remains, including Aboriginal ones, from a group of leading historians, museum directors, lawyers, anthropologists and medical specialists. The group, chaired by Professor Norman Palmer, a legal academic from University College, London, is understood to have found that at least two-thirds of British museums hold remains.

European and British museums are believed to hold several thousand Aboriginal bones, and quantities of hair and soft tissues, removed from Australia usually against the wishes of local people or without their knowledge.

Two years ago the Prime Minister, John Howard, and the British Prime Minister, Tony Blair, agreed to speed up the return of human remains between the two countries, but several institutions, including the Natural History Museum in London, oppose the idea.

But there have been some recent repatriations, including the return by the British Royal College of Surgeons of several remains of Truganini, one of colonial Australia's most famous Aboriginal figures.

The Aboriginal and Torres Strait Islander Commissioner, Rodney Dillon, said the repatriation of remains was decided by each institution that held them. "It's very delicate for Aboriginal people and very hard to deal with. We're talking about people's grandmothers and grandfathers."