Sydney, Sept 9 (ZEENEWS.COM) Australia agreed Friday to buy US-sourced long-range missiles for its ageing fleet of F/A-18 Hornet fighter planes.

The Australian Defence Force (ADF) said it had signed an agreement with Lockheed Martin for AGM-158 joint air-to-surface stand-off missiles in a deal worth more than 300 million dollars (225 million US).

The ADF said the deal was made possible under a foreign military sales agreement with the US government.

It said the missiles, which have a range of 200 nautical miles (370 kilometres), would be operational on the planes by 2009.

"(The missile's) significant stand-off range will enable aircrews to conduct strike missions from outside the engagement ranges of hostile air defence systems likely to be encountered in the foreseeable future," the ADF said.

The F/A-18 has been Australia's main fighter for more than 20 years and the fleet is scheduled for retirement in 2015.

However there are doubts about the timetable because of delays with its replacement, the F-35 Joint Strike Fighter (JSF), which is still being developed in the United States.

Australia is a close ally of Washington, participating in the US-led campaigns in Iraq and Afghanistan, and sources much of its defence hardware from the United States.