Image copyright AFP Image caption Mr Abbott said the drones are essential to Australia's national security

Australia has announced it will buy unmanned surveillance drones from the US to protect its borders and commercial interests.

The fleet, to be based in Adelaide, would provide the defence force "with unprecedented maritime surveillance capabilities", PM Tony Abbott said.

The drones would also be used to protect energy resources, he added.

The drones, which are still being tested by the US navy, can remain airborne for up to 33 hours.

The number of drones to be purchased is yet to be determined.

"We do need to have a strong defence - national security is as important as economic security when it comes to the good government of our country," Mr Abbott said.

"Given that Australia has responsibility for something like 11% of the world's oceans, it's very important that we've got a very effective maritime surveillance capability."

The MQ-4C Triton drones, which are unmanned aerial vehicles used for surveillance, can cruise at altitudes up to 55,000 feet.

The vehicle's size is comparable to a small aircraft with a wingspan of 40 metres (131 feet), Reuters news agency says.

In Australia, the drones are to be stationed at Adelaide's air force base.

Mr Abbott said the purchase plan would boost South Australia's economy with about A$100m ($90m, £54m) in investments.

The announcement comes as Australia steps up its maritime border patrols to deter asylum seekers arriving by boat from neighbouring Indonesia.