Australia will send 200 troops to the Middle East to protect crucial oil supplies from Iranian forces in a mission Prime Minister Scott Morrison concedes may extend beyond the initial six-month deployment.

After weeks of deliberations by the national security committee of cabinet, specialist personnel will now work to formalise the rules of engagement before an Australian Defence Force frigate and surveillance aircraft arrive in the increasingly hostile Strait of Hormuz later this year.

The Prime Minister slammed Iran's harassment of commercial oil tankers as"destabilising behaviour" and a threat to Australia's national interests.

"This is a modest, meaningful, and time-limited contribution that we are seeking to make to this international effort," Mr Morrison said at Parliament House on Wednesday.