Australia has admitted it has returned 41 asylum seekers to the Sri Lankan authorities at sea, raising concerns that it violated international law.
The transfer took place on Sunday.
Rights groups had raised concerns that some 200 Sri Lankans may have been handed over, including Tamils who say they face persecution at home.
The government has not commented on other possible cases, but says everyone was subject to “enhanced screening” to ensure compliance with Australia’s international obligations.
This is the first time the Australian government has confirmed it has intercepted people at sea, screened them and returned them to their country of origin. Immigration Minister Scott Morrison acknowledge on Monday that a boat-load of 41 people had been handed back to Sri Lanka, while not commenting on the fate of a second boat reportedly carrying about 150 people.
Scott Morrison said they were transferred at sea just outside the Sri Lankan port of Batticaloa on Sunday.
“All persons intercepted and returned were subjected to an enhanced screening process,” he said.
The government says only four of those returned on Sunday were Tamils.
Scott Morrison added that only one person may have had a case for asylum but he opted to return voluntarily with the rest of the passengers.
Last week the UN refugee agency UNHCR had expressed “profound concern” about the reported situation.
“Requests for international protection should be considered within the territory of the intercepting state, consistent with fundamental refugee protection principles,” it said.
“International law prescribes that no individual can be returned involuntarily to a country in which he or she has a well-founded fear of persecution.”
Sri Lanka has been under heavy international pressure over alleged human rights violations during the final phase of the war against Tamil separatists which ended in 2009.
Rights groups say Tamils still face violence at the hands of the military.
The Australian government has been criticized for imposing what campaigners call a culture of secrecy around asylum, by refusing to comment on operations.
Under current policy, asylum seekers who arrive by boat are sent to detention camps in Papua New Guinea (PNG) or Nauru. If found to be refugees, they will be resettled there, not in Australia.
Australia says its asylum policy – which is also widely believed to involve towing boats back to Indonesian waters – is aimed at saving lives.
It is also facing tough questions over its offshore processing policy. The UN and rights groups have condemned conditions in its camps in PNG and Nauru.