An Australian court's gagging order banning the reporting of allegations against several foreign political leaders in a major bribery scandal was Thursday slammed as unacceptable by activists and media groups.

Details of the suppression order, imposed by the Victorian Supreme Court in Melbourne on June 19, were revealed by whistleblowing website WikiLeaks.

It relates to an ongoing investigation into allegations that Asian officials and their families were bribed to secure contracts to print their currencies by a company -- Securency -- linked to Australia's central bank.

The Australian Broadcasting Corporation said the gag was issued after the Department of Foreign Affairs and Trade stepped in, arguing that publication of the names could affect national security and international relations.

WikiLeaks founder Julian Assange called it the largest "blanket suppression order" since 1995, when Australia sought to prevent publication of details around a joint US-Australian intelligence spying operation against the Chinese embassy in Canberra.

"With this order, the worst in living memory, the Australian government is not just gagging the Australian press, it is blindfolding the Australian public," said the former computer hacker, himself an Australian.

"This is not simply a question of the Australian government failing to give this international corruption case the public scrutiny it is due.

"The concept of 'national security' is not meant to serve as a blanket phrase to cover up serious corruption allegations involving government officials, in Australia or elsewhere."

France-based Reporters Without Borders spokesman Benjamin Ismail said the order spoke "volumes about the current level of transparency in Australia".

"The grounds given for this gagging order, which include national security, are unacceptable and cannot justify such complete censorship applying to all news and information providers, including both journalists and ordinary citizens," he said.

"We urge the authorities to put the public interest above national interest and to restore transparency in this case by rescinding this order at once."

The Australian government has not commented but Sydney-based lawyer Michael Bradley told the ABC that in the age of the Internet, such suppression orders were futile.

"I think they can only ever realistically have temporary effect and the degree of interest that they generate once they become known tends to enhance the amount of publicity that's attracted to the underlying issue, because it's a guessing game and it's entertaining and fun," he said.

"I think they're ultimately self-defeating."

The gag order was the latest revelation by WikiLeaks, which angered the United States in 2010 by publishing hundreds of thousands of classified documents on the wars in Iraq and Afghanistan.

It also released a huge cache of US diplomatic cables that embarrassed governments worldwide.

Assange is currently holed up in the Ecuadorian embassy in London to avoid extradition to Sweden to face sexual assault claims.

He denies the claims and fears that if he goes to Sweden he will be sent to the United States to face charges for publishing classified material.