A police fact sheet submitted in court here also alleged that the spiritual leader of the 18 Muslims arrested in Sydney and Melbourne urged his followers to unleash "maximum damage" as part of a holy war.

The 20-page document, tendered in court on Friday but not released to the public until Monday, said three of the 18 had been stopped by police acting suspiciously near the Lucas Heights research reactor in suburban Sydney.

The men said they were in the area to ride a trail bike that was in the back of their car, but when questioned separately gave differing accounts of their activities, police said.

Police later found that a lock on a gate to a reservoir on the grounds of the facility had recently been cut, the document said.

The government's Australian Nuclear Science and Technology Organisation (ANSTO), which operates the Sydney reactor, played down any threat.

ANSTO issued a statement saying the area where the men's car was noticed "is regularly used by the public for trail bike riding and bushwalking" and that security agencies at the time did not see the trio as a threat.

It also said the fencing that had been cut near the reservoir was hundreds of meters from the reactor and not part of the ANSTO facility.

Police and security agents detained the 18 before dawn on November 8 in the country's biggest counter-terrorism operation.

All were Australian-born or naturalised citizens. Officials accused them of plotting a "catastrophic" act of terrorism, although no precise targets were alleged.

The arrests heightened security fears across Australia and sparked an extraordinary terrorism alert Monday in the third largest city, Brisbane.

Authorities in the east coast city announced in mid-afternoon that all public buses and trains would unload their passengers for 30 minutes during the evening rush hour due to three anonymous telephone threats.

Local officials said they ordered the "overly cautious" reaction due to heightened security concerns following the arrests in Sydney and Melbourne.

The 30-minute transport shutdown went off without incident and the threats appeared to have been a hoax.

The 18 detained suspects have been charged with membership in a terrorist organisation and/or stockpiling explosives components in preparation for a terrorist act.

In the list of allegations released Monday, police said they were linked to an extremist group led by a Melbourne Muslim cleric, Abdul Nacer Benbrika, also known as Abu Bakr, who was among those detained.

"Benbrika is a Muslim extremist and has publicly declared his support of a violent jihad," it said, adding that the cleric had "a core group of followers in Melbourne who are associated with the persons of interest in Sydney."

Police quoted Benbrika as telling some of the suspects during a meeting in February that if they wanted to "die for jihad, we have to have maximum damage".

"Damage their buildings, everything. Damage their lives to show them," he allegedly said, in statements obtained through electronic eavesdropping. "In this we'll have to be careful."

Six of the Sydney suspects allegedly underwent military-style training early this year at two properties near Bourke in the far west of New South Wales state, the report said.

"Police allege that these camping and hunting trips are part of the jihad training being undertaken by this group," it said.

"These trips are consistent with the usual modus operandi of terrorists prior to attacks."

Police also said they found large quantities of detonators and various chemicals used to make explosives during searches of the suspects' homes.

They also allegedly found guns, numerous mobile phones, backpacks, latex gloves, videos on "jihad" and a computer memory stick containing instructions in Arabic on how to make explosives using household chemicals.

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