(CNN)More than 65 years since the UK began conducting secret nuclear weapons testing in the Australian Outback, scores of files about the program have been withdrawn from the country's National Archives without explanation.
Review or 'cover up'? Mystery as Australia nuclear weapons tests files withdrawn
The unannounced move came as a shock to many researchers and historians who rely on the files and have been campaigning to unseal the small number which remain classified.
"Many relevant UK documents have remained secret since the time of the tests, well past the conventional 30 years that government documents are normally withheld," said expert Elizabeth Tynan, author of "Atomic Thunder: The Maralinga Story".
"To now withdraw previously available documents is extremely unfortunate and hints at an attempted cover-up."
Withdrawal of the files was first noted in late December. Access to them has remained closed in the new year.