Important rights and freedoms are at risk of being “chipped away” in Australia, the United Nations special rapporteur for freedom of expression has warned.

In an interview with Guardian Australia, David Kaye said laws restricting reporting on asylum seeker policies were “a real threat” to sources and whistleblowers.

“You see in Australia the restrictions on sources and reporters who might want to report about the migrant detention situation,” Kaye said. “And there might be some situations, perhaps based on privacy, where some information should not be released, and the restrictions on the disclosure might be legitimate.

“But blanket restrictions on an area of policy that is really of great importance to the public, I think that’s a real threat to sources. It’s also a threat to whistleblowers.”

Kaye said Australia had some strong protections, but there was growing concern about government overreach.

“On the one hand Australia has a very strong framework for freedom of information, and for whistleblower protection. The concern that I have, and I think that I’ve seen expressed by civil society and by journalists in Australia, is that those protections which are strong in law are being eroded, particularly in the context of the migration detention and surveillance issues.

“Those kinds of threats we’re definitely mindful of. On paper Australia has a very a strong set of norms. The question is: are they chipped away by these other interests and legal efforts that we’re seeing?”

News stories about asylum seekers – including some from Guardian Australia – have been referred to the Australian federal police for investigation with a view to prosecuting their sources. The Border Force Act, introduced in July, criminalises the disclosure of information by staff who work in immigration detention centres.

In September a senior UN human rights official, François Crépeau, cancelled a visit to Australia after the government failed to guarantee it would not seek reprisals against anyone who spoke to him.

Kaye’s latest report, released on Tuesday, urges nations to adopt stronger frameworks to protect whistleblowers and confidential sources.

The report was published on the same day that Australia began a data retention scheme under which telecommunications companies must retain a vast amount of phone and web data for two years.