Edward Snowden and Bradley Manning should not be regarded as whistleblowers as the information they made public did not expose government wrongdoing, the Australian attorney general said.

Speaking on Tuesday to the Security in Government Conference in Canberra, Mark Dreyfus also defended Australia's own telecommunications interception programme.

In his most direct comments to date on the impact of the Guardian's revelations about the US National Security Agency surveillance, Dreyfus expressed concern that Snowden's leaks might cause "long-lasting harm" to Australia's ability to "respond to the many threats that our nation faces". He stopped short of giving any detail on what harm the disclosures might have.

Dreyfus described the leaks as "politically motivated". He said: "Some people have suggested that all of the disclosures by Mr Snowden and Mr Manning were some kind of 'whistleblowing'. Where an activity has been authorised under law and overseen by appropriate government bodies and where no wrongdoing has been identified, the disclosure of information is not 'whistleblowing'."

Defending Australia's interception programme, he said: "I want to reiterate that Australia's intelligence activities are carried out in a manner that is consistent with our law, and for the purpose of protecting Australia's democratic values."

He added that intelligence services' access to telecommunications had resulted in 5,928 prosecutions and 2,267 convictions based on "lawfully intercepted material" in the 2011-12 financial year. "Most of those were for serious criminal offences," he said.

During that 12 months there were 293,501 disclosures of metadata to a range of governmental and non-governmental organisations under the Telecommunications Act, meaning that just 0.7% of disclosures resulted in prosecution.

The Greens communications spokesman, Senator Scott Ludlam, said Dreyfus's attack on Manning and Snowden "beggars belief". The attorney general was making a "decisive statement in the defence of spying on law-abiding citizens, in the defence of universal surveillance", he said.

Senator Ludlam, who introduced a bill to parliament aimed at tightening the government's ability to intercept telecommunications data, added: "If the attorney general believes ... that the operation of the PRISM surveillance system does not constitute 'wrongdoing' – then it bodes badly for Australia. If the attorney general believes Bradley Manning did not reveal 'wrongdoing', then what does it take before someone is permitted to blow the whistle?"

Dreyfus's comments sit uncomfortably with a move to bolster and unify shield laws for journalists and whistleblower protection for public servants. In June he announced plans to unify shield laws across the states, which he described as inadequate in some parts of Australia.

"Journalists need to be confident that they can protect the identity of their sources without being held in contempt of court," he said at the time.

The attorney general also introduced the Public Interest Disclosure Act in July, which was described as offering a "historic level of protection" to federal public servants who disclose wrongdoing.