The commander of Australia’s anti-people smuggling Operation Sovereign Borders, Major General Andrew Bottrell, said Monday the figure had now risen to 18.

This includes a boatload of 46 people returned to Vietnam, reportedly on an Australian navy vessel, in April.

Bottrell gave few details of the military-led operations.

“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,” Bottrell said.

“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.”

Since July 2013 Australia has sent asylum-seekers arriving on boats to detention centres on Papua New Guinea’s Manus Island and on Nauru.

They are denied resettlement in Australia even if they are subsequently found to be genuine refugees.

Canberra has said the policies are necessary to stop asylum-seekers entering Australia by boat. They had previously been arriving almost daily in often unsafe wooden fishing vessels, with hundreds drowning en route.

The development comes as southeast Asia grapples with an exodus of boat people fleeing persecution and poverty, with possibly thousands of migrants feared stranded at sea.