Asylum seekers who were returned to Vietnam by the Australian Navy last week are believed to be being interrogated at a police-run detention centre in a coastal province north of Ho Chi Minh City.

According to sources in the Australian Vietnamese community, all adults who were on-board a boat intercepted somewhere north of Australia have been detained for questioning for the past week.

It is also believed that they left southern Vietnam in March – meaning Australian authorities potentially kept the group detained for weeks while their asylum claims were screened by Immigration Department officials on-board the HMAS Choules.

They were handed over to officials in Vung Tau, a southern port city, last Friday. Immigration Minister Peter Dutton confirmed for the first time on Thursday that 46 people had been returned.