Immigration Minister Peter Dutton told reporters in Brisbane on Wednesday, the boat carrying 21 men, women and children on board were processed at sea and then flown home.

“They claimed that they were wanting protection. It was found that they weren’t owed protection and they were returned back to Vietnam,” he said.

The boat, discovered by the Navy earlier this month in the Timor Sea, is the third from Vietnam to be intercepted by Australian authorities in the past 14 months.

The latest incident is the 28th known boat turn-back since the conservatives came to power in 2013. It is also the first boat arrival since the start of this election campaign.

Mr Dutton has warned Australians not to be complacent about asylum-seeker boat arrivals in the wake of the latest turnback.

“People who think this problem has gone away, please don’t believe that,” Mr Dutton said, pointing to the humanitarian crisis in Europe and the Mediterranean Sea.

A UN refugee agency report released this week put the number of displaced people, refugees and asylum seekers worldwide at more than 65 million.

“Potentially (they) could come to a country like ours tomorrow,” Mr Dutton said.

Under Canberra’s tough measures, asylum-seekers trying to reach Australia by boat are either sent back to where they departed or to remote Pacific island camps, where living conditions have been criticised.

– with other agencies