(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began conducting secret nuclear weapons testing in the Australian Outback, scores of files about the program have been withdrawn from the country's National Archives without explanation.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 Mystery as Australia nuclear weapons tests files withdrawn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.
The UK conducted 12 nuclear weapons tests in Australia in the 1950s and 1960s, mostly in the sparsely populated Outback of South Australia.
Information about the tests remained a tightly held secret for decades. It wasn't until a Royal Commission was formed in 1984 -- in the wake of several damning press reports -- that the damage done to indigenous people and the Australian servicemen and women who worked on the testing grounds became widely known.
Indigenous people living nearby had long complained of the effects they suffered, including after a "black mist" settled over one camp near Maralinga in the wake of the Totem I test in October 1953. The mist caused stinging eyes and skin rashes. Others vomited and suffered from diarrhea.
These claims were dismissed and ridiculed by officials for decades -- until, in the wake of the Royal Commission report, the UK agreed to pay the Australian government and the traditional owners of the Maralinga lands about AU$46 million ($30 million). The Australian authorities also paid indigenous Maralinga communities a settlement of AU$13.5 million ($9 million).
While the damage done to indigenous communities was acknowledged, much about the Totem I test -- and other tests at Maralinga and later at Emu Field -- remained secret, even before the recent withdrawal of archive documents.