AUSTRALIA secretly worked with the United States to weaken a key international treaty to ban cluster bombs, leaked US diplomatic cables show.

Despite taking a high-profile stance against cluster munitions - condemned as the cause of large numbers of civilian casualties - Australia was privately prepared to pull out of international negotiations on a global ban of the weapons if this threatened ties with US forces.

A cluster mortar. Credit:AFP

The US continues to use cluster munitions as ''a legitimate and useful weapon'', including in Afghanistan, and has affirmed that it will not sign the treaty to ban them. The disclosure comes as Federal Parliament prepares to consider a bill to ratify Australia's signature of the Convention on Cluster Munitions.

The draft legislation has attracted sharp criticism from non-government organisations for not matching the spirit of the treaty. One US group complained the legislation could be interpreted to ''allow Australian military personnel to load and aim the gun, so long as they did not pull the trigger''.