The government has admitted the need to secure oil supplies is a factor in Australia's continued military involvement in Iraq.

Defence Minister Brendan Nelson said today oil was a factor in Australia's contribution to the unpopular war, as "energy security" and stability in the Middle East would be crucial to the nation's future.

Speaking ahead of a key foreign policy speech today by Prime Minister John Howard, Dr Nelson said defence was about protecting the economy as well as physical security, and it was important to support the "prestige" of the US and UK.