The men arrested have links to the Somali-based terrorist group al-Shabaab, which the government indicated would now be added to a list of banned groups that includes Al Qaeda and other Islamist terrorist organisations.

'This has been the subject of some internal deliberations within the government,' Prime Minister Kevin Rudd said.

The prime minister also ordered a review of security at military bases. At Holsworthy, as elsewhere, the gates are manned by unarmed security guards provided by private firms.

Nayef al-Sayed, 25, the first of the five men in custody to appear in court to be formally charged with committing an act in preparation for a terrorist act, refused to stand in the courtroom during Tuesday's appearance, saying his religious beliefs prevented him from doing so.