The United Nations refugee agency has revealed a group of Vietnamese asylum seekers had their claims assessed at sea before being returned home by the Australian Navy.

The group of 46 asylum seekers were returned by the Navy to Vietnam, and the UNHCR said they were subject to a screening process at sea.

The agency said it was seeking details from the Government about the procedures used but has expressed its concern.

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UNHCR spokeswoman Vivian Tan said the agency considers that individuals who seek asylum must be properly and individually screened for protection in an environment where they can explain their needs, or they could be at risk of grave danger.

“We’re concerned that people may not have had access to proper procedures,” she said.

“We are concerned that the group wasn’t screened and assessed in a way that’s fair and affective, that somehow their lives may be at risk.”

Human Rights Watch deputy director Phil Robertson said he was “very suspect” about the way the operation was conducted.

“I think that probably these people had no access to counsel or [were] able to prepare their case. And certainly they had no access to appeal,” he said.

“So it’s a shoddy process determined to send people back and that’s what’s happening to these group of Vietnamese.”

Mr Robertson said there remains legitimate reason for Vietnamese nationals to seek asylum.

“Vietnam is still a dictatorial one-party state and there are many people in Vietnam who have run afoul of the Vietnam government for inserting freedom of religion, for blogging, for trying to defend their land against encroachment by the state,” he said.

“It goes on and on. There’s over 200 political prisoners in Vietnam.”

The ABC confirmed HMAS Choules had completed its mission to transfer the group back to Vietnam.

Another source told the ABC the 46 asylum seekers were offloaded in the port city of Vung Tau on Friday.

The asylum seekers were believed to have left Vietnam in March and were detected by the Navy earlier this month before they could reach Australia.

The Opposition has accused the Federal Government of a “new low” over secrecy surrounding the group of asylum seekers.

The Government has said it will not comment on operation matters.

– ABC