Dutton coy on returning Vietnamese

Immigration Minister Peter Dutton is maintaining his silence about reports Australia has forcibly returned 50 asylum seekers to Vietnam.

An Australian Navy ship reportedly travelled to Vietnam late last week as part of a secret border operation.

Mr Dutton told ABC radio on Monday he would release details publicly at an appropriate time.

Opposition immigration spokesman Richard Marles said the minister's secrecy represented a new low.

He called on Mr Dutton to explain what assessments of claims by asylum seekers had taken place and guarantee they were undertaken individually.

"We need to have confidence that this government has not refouled people against the obligations of the UN convention," he told ABC Radio.