Australia’s attorney general, George Brandis, has told a Senate committee he is unable to provide confidential details to substantiate his claim that disclosures by the former US intelligence contractor Edward Snowden have put lives at risk.

Brandis also said on Monday he had no hesitation in describing Snowden as a “traitor”, arguing the National Security Agency (NSA) leaker had betrayed his country and prejudiced the interests of its intelligence partners.

The issue was raised by the Greens senator, Scott Ludlam, who has previously clashed with Brandis over the significance of Snowden’s leaks about the extent of western intelligence-gathering and surveillance programs.

The disclosures, published by the Guardian and other media, led the US president, Barack Obama, to commission a review, which recommended in December a number of reforms including an end to the NSA’s practice of collecting telephone records in bulk.

During the Senate estimates hearing in Canberra, Ludlam asked if Brandis could identify a single case of a life having been put in danger by the revelations.

Brandis, who has previously argued Australian lives were among those put at risk, replied: “You ask me if I’m aware of particular cases; the answer to your question is yes, on the basis of intelligence briefings I receive.”

Ludlam said the attorney general had failed to substantiate the claim: “We’ll just have to take your word for it.”

Brandis said that under no circumstances would any Australian government reveal information from private intelligence briefings.

Brandis accused Ludlam of describing Snowden as a whistleblower “for rhetorical purposes”, arguing the former NSA contractor “satisfies none of the tests of a whistleblower” under US or Australian law.

The attorney general denied he was using the word traitor for rhetorical purposes, saying the description was based on “numerous admissions as to his own conduct”.

“If somebody admits to conduct then it is perfectly appropriate in my view, without being rhetorical, to characterise that conduct for what it is,” Brandis said.

Brandis said if Snowden were ever to return to the US from Russia and were to be put on trial, an American jury would not be prejudiced by any statements he had made.

“I believe that Mr Snowden betrayed his country, he betrayed the United States of America by putting into the public domain extensive highly classified material that prejudiced the interests of the United States and its intelligence partners in very important ways.”

Obama has criticised Snowden’s actions, saying US defences depended “in part on the fidelity of those entrusted with our nation’s secrets”.

But the president said last month that the resulting debate over government surveillance was important and would “make us stronger”.

Australia’s relationship with Indonesia came under strain in November after Guardian Australia and the ABC revealed that a November 2009 document leaked by Snowden showed spy agencies had attempted to listen in on the personal phone calls of the Indonesian president, Susilo Bambang Yudhoyono, and targeted the mobile phones of his wife, senior ministers and confidants.