There has been a heightened level of "terrorist chatter" in the aftermath of the Sydney siege tragedy, Prime Minister Tony Abbott says.
Mr Abbott said the national security committee of cabinet received intelligence from security agencies on Tuesday of the increased "chatter" amongst terrorist sympathisers.
He didn't identify a possible target.
The terror threat level hasn't been lifted, and remains at high.
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"At this level an attack is likely," the prime minister told reporters in Sydney.
"We don't know when and how an attack may come, but we do know there are people with the intent and capability to carry out further attacks."
Mr Abbott assured the public that police and security agencies would be highly active and visible during the Christmas holiday period.
But general public should be aware of the "reality of these times", he said.
"There are people out there with evil intentions and we will do everything we humanly can to protect you from them," Mr Abbott said.
