Secret defence documents of Australia's most senior commander in the Middle East, Maj. Gen. John Cantwell, were contained in a USB drive that was stolen from his aide's checked in bag at Kuwait's airport on Feb. 28, a military investigation has found.

The Defence Security Agency investigation report, which The Age revealed Friday, described the theft as a major security breach. The lost Cantwell files were downloaded from the Defence Secret Network.

Cantwell's aide, who was not named, violated security measures when he placed the thumb drive storage device inside a zippered pocket of his unlockable backpack during a flight from Dubai to Pakistan, where Cantwell was to meet with Pakistani officials, the report said.

The bags of passengers in the same flight as Cantwell, the aide and another officer went missing upon their arrival in Islamabad but were returned untouched after several days. But the aide could no longer find the USB and a pair of sunglasses in his backpack.

The DSA investigators suspect that foreign intelligence agents stole the device.

No disciplinary action was imposed on the aide, a defence spokeswoman said.

The report recommended a review of the Middle East travel policy for military officials to prevent foreign intelligence agents from stealing information from them.

Major-General John Cantwell with an explosive detection dog at the Australian forces staging area in the UAE on Dec. 8, 2010.