The federal government has defended the level of scrutiny of its offshore migrant detention centres after the human rights commissioner was advised she had no jurisdiction to visit them.

Commissioner Gillian Triggs has received initial legal advice from the Solicitor-General that she cannot visit Nauru or Papua New Guinea's Manus Island to assess complaints from asylum seekers about conditions there.

Her office is understood to be seeking more information and confirmation of the legal position.

The United Nations High Commissioner for Refugees has visited the centres and released scathing reports, describing the conditions there as harsh and troubling.

On Tuesday, Immigration Minister Brendan O'Connor said Professor Triggs had earlier told him she was "relaxed" about determining whether she could visit the centres as she would not want to act beyond her powers.

He said the UN High Commissioner for Refugees had visited the Manus centre, so had the Red Cross, the shadow minister immigration minister and Greens Senator Sarah Hanson-Young.

"It's not a place that's without scrutiny," the minister told reporters in Sydney on Tuesday.

"There's been quite good access, and it really is for the matter to be determined as to whether there's jurisdiction for the human rights commissioner," he said.