The government on Thursday sent 39 Sri Lankans home on a charter flight, including 38 of the 66 asylum seekers who arrived in Geraldton after 44 days at sea last week.

The group was sent back after being subject to ''enhanced screening'' processes, in which people are ''screened out'' of the refugee determination process, before they have entered into the formal processing period.

Mr O'Connor said authorities had found no evidence that those who were returned were genuine refugees.

And he defended his department over revelations some of those asylum seekers forcibly returned did not meet with lawyers to help them understand the screening process.

''I've been advised those that have not been provided with legal advice did not seek legal advice,'' Mr O'Connor said. ''In these individual circumstances they did not engage our international obligations.''

Mr O'Connor did not directly respond when he was asked on Friday why all asylum seekers had not been afforded access to lawyers even if they did not know to ask for one.

Women and children were among those sent home, Mr O'Connor said, after authorities had determined they did not have genuine claims for refugee status in Australia.

But refugee advocates described the process as an abuse of process and unlawful.

Refugee lawyer David Manne, who successfully led the High Court challenge against the government's Malaysia solution, said the expulsions were ''a radical retreat'' from long-standing laws and practices in Australia.

''Did Govt tell Geraldton arrivals of their statutory rights to legal advice and to apply for protection under due process?'' Mr Manne asked on Twitter. ''If not, why not?''

Asylum Seeker Resource Centre chief executive Kon Karapanagiotidis wrote on Twitter that the asylum seekers never had a chance of a fair assessment. ''In 12 years of working with asylum seekers, this is the worst abuse I have seen … deporting people with no access to legal advice/representation doesn't get any more unlawful.''

Mr O'Connor said with 46 million displaced people around the world, Australia as a wealthy nation had ''an obligation to assist''. ''But we must ensure that when we dedicate resources to provide places for people fleeing persecution that those places must be filled with people who are genuinely fleeing persecution.''

Australian Human Rights Commissioner Gillian Triggs said she was ''profoundly concerned'' about the forced returns.

"The commission understands that these people were subjected to an 'enhanced screening process' that has been used in recent months exclusively for unauthorised maritime arrivals from Sri Lanka," Professor Triggs said.

"If the claims of asylum seekers are not properly assessed, Australia risks breaching its non-refoulement obligations.''