Aboriginal artefacts, including two early bark etchings, have been seized in Australia while on loan from two British museums.
Members of the Dja Dja Wurrung tribe secured an emergency order preventing the items being returned to the British Museum and the Royal Botanic Gardens.
The two bark etchings and a Aboriginal ceremonial headdress were on loan to Museum Victoria in Melbourne.
Gary Murray, of the Dja Dja, accused the museums of "colonial arrogance".
He told BBC News Online the fragile bark etchings, which were made in around 1845 by members of the Dja Dja Wurrung tribe in the Wimmera district of western Victoria, were part of their cultural heritage.
The artefacts were due to be returned to the British Museum and the Royal Botanic Gardens at Kew, south west London, last week, but the Dja Dja Wurrung Native Title Group sought an emergency declaration under an aboriginal heritage protection law. The order can be renewed indefinitely.
The group has applied to Victoria's state minister for a permanent order.
Mr Murray said: "It's not British culture we are talking about here, we are talking about our rights as a first nation.
"We believe strongly that they connect us to our country, our culture and ancestry.
"If you haven't got a past then you haven't got a future and it is our future at stake here."
The etchings, one depicting men carrying boomerangs while the second shows a hunting scene, were on loan to Museum Victoria for its 150th anniversary exhibition, Etched On Bark 1854.
Patrick Greene, chief executive officer of Museum Victoria, said the emergency declarations "came really out of the blue".
He said: "First of all, we have a contractual arrangement with the British Museum and the Royal Botanical Gardens at Kew and we will stand by that and we will do everything to make sure that we do comply with that and return the items.
"The second priority is to ensure that our relations with the Aboriginal community - which are very good and which have been built up over many years - also remain good."
But Mr Murray added: "We are not going to be bullied and we are going to stand firm on this.
"We have had legal advice and representation and we are prepared to exert our Australian legal rights.
"If the British found the Crown Jewels in Australia they would be sending the warships in to get them back.
"We are trying to do this in a fair-minded way. We are not holding anyone to ransom and we are not hijacking art."
In a joint statement, the Royal Botanical Gardens and the British Museum said it was important to continue lending objects to exhibitions around the world.
"The objects lent by the British Museum and Kew to the Museum Victoria exhibition 'Etched on Bark' are part of a growing programme of worldwide loans from both institutions.
"Exhibitions of this kind, bringing rare material from collections throughout the world, provide invaluable opportunities to make available to the world public the latest research and interpretations of the objects and the human cultures that produced them.
"The emergency declaration puts at risk the very legal framework that allows such exhibitions to take place drawing on loans from Europe and America."