Australia turned back 28 asylum seeker boats in 3 years

In this May, 2013 photo, Iranian asylum seekers, who were caught in Indonesian waters while sailing to Australia, sit on a boat at Benoa port in Bali, Indonesia.

The Australian government says it has turned back 28 boats to prevent asylum seekers from reaching Australia during three years in power, with the latest carrying 21 Vietnamese intercepted this month.

The conservative coalition government on Wednesday warned that the boats would start coming from Indonesian ports in greater numbers if the centre-left Labour Party wins a national election set for July 2.

Border Protection Minister Peter Dutton said the 21 Vietnamese, including four children, were returned to Vietnam after their refugee claims were assessed and rejected at sea. He declined to give details of the interception.

Opposition leader Bill Shorten says a Labour government would maintain the same tough policies that have prevented many asylum seekers from reaching Australia by boat for two years.