Eighteen asylum-seeker boats have been stopped from reaching Australia since Operation Sovereign Borders began, including one "take-back" completed last month.
The commander of Operation Sovereign Borders, Major General Andrew Bottrell, has confirmed a boat carrying 46 Vietnamese was returned to Vietnam on April 18.
It's understood the asylum seekers were off-loaded by an Australian Navy vessel in the port city of Vung Tau, after leaving Vietnam for Australia in March.
Another boat was the subject of a "turn-back" that was completed on March 22. Details of the number of asylum seekers aboard the vessel have not been revealed.
Maj Gen Bottrell confirmed a total of 18 asylum-seeker boats had been prevented from reaching Australia since September 2013, when the Abbott government introduced Operation Sovereign Borders to tackle the people-smuggling trade.
However, he refused to release further details, saying he would be maintaining the cloak of secrecy surrounding the operation, which the government insists is needed to ensure the integrity of missions.
"While I'm acutely aware of the interest surrounding the release of information, the success of Operation Sovereign Borders has been in part due to the denial of operational information from people-smugglers," Maj Gen Bottrell said.
Maj Gen Bottrell warned people smugglers were still actively trying to sell passage to Australia.
"Despite the results achieved under Operation Sovereign Borders to date, people-smugglers continue to try to take advantage of vulnerable people by convincing them to get on boats to Australia," he said.
