Australian media firms rallied behind WikiLeaks founder Julian Assange yesterday and warned they would “strongly resist” moves to outlaw or prosecute publication of his website’s material.

The country’s newspaper and television chiefs issued an open letter condemning Canberra’s “deeply troubling” response to Australian-born Assange’s dumping of some US diplomatic cables on the internet. Prime Minister Julia Gillard has rounded on Assange and WikiLeaks as grossly irresponsible and “illegal”, and the government has said it has considered cancelling his passport.

Describing the whistleblowing WikiLeaks site as a “part of the media”, the letter said there was no evidence the cables had endangered national security or individuals, or that Assange or WikiLeaks had broken Australian law. “We will strongly resist any attempts to make the publication of these or similar documents illegal,” read the letter to Ms Gillard.

“Any such action would impact not only on WikiLeaks, but every media organisation in the world that aims to inform the public about decisions made on their behalf.”

While the volume of the leaked correspondence was “unprecedented” the letter said publishing diplomatic communication was nothing new and WikiLeaks was doing what the media had always done: “Bringing to light material that governments would prefer to keep secret”.

The news directors and editors said WikiLeaks had “no doubt made errors” but said it had given global citizens an insight into Washington’s thinking on “some of the most complex foreign policy issues of our age”.

“It is the media’s duty to responsibly report such material if it comes into their possession,” the letter said. “To aggressively attempt to shut WikiLeaks down, to threaten to prosecute those who publish official leaks, and to pressure companies to cease doing commercial business with WikiLeaks, is a serious threat to democracy, which relies on a free and fearless press.”

Australia has been featured in a number of embarrassing cables from the site, including one in which the then prime minister Kevin Rudd, now Foreign Minister, urged the US to consider using force against China if necessary.