Nearly half of Australia's navy patrol boats that detect asylum-seekers are out of service

SYDNEY (AFP) - Nearly half of the Australian navy patrol boats used to detect asylum-seekers have been confined to port with structural cracks, a report said on Tuesday, but the government insisted its Operation Sovereign Borders continued as normal.

Under Canberra's hardline immigration policy, would-be refugees arriving by boat can be turned back at sea to Indonesia where many board rickety vessels to make the perilous crossing to Australia.

Large cracks were discovered in six of the 14-strong Armidale fleet 10 days ago, forcing the ships back to port in Darwin, The Australian newspaper reported.

But Australia's Immigration Minister Scott Morrison said the military-run operation was unaffected by the problem.

"This is not affecting Operation Sovereign Borders - any vessels that seek to illegally enter Australia will be intercepted and safely removed from our waters," a spokesman for Mr Morrison said in a statement, without confirming how many boats were affected.

The fleet, built in Australia between 2004 and 2007, faced similar problems two years ago.

"Maintenance issues such as this are not unexpected when operating a significant number of maritime assets in a wide range of demanding environments," the spokesman said, adding that other "appropriate assets" were being used.

The Australian said the military was supposed to provide seven patrol boats from the Armidale fleet each day as part of Operation Sovereign Borders, but had only been able to send four.

The impact has been softened by fewer boats arriving since the operation was launched by Australia's conservative government last year.

Hundreds of asylum-seekers have died making the dangerous sea voyage from Indonesia to Australia in recent years, prompting the so-called Sovereign Borders crackdown.

The policy appears to be working with no arrivals in more than two months, although it has angered Jakarta which has suggested it could infringe the country's sovereignty, and prompted criticism from rights groups.