SYDNEY -- Two men have been arrested in Sydney as part of a counter-terrorism operation, police said on Wednesday.

A 20-year-old man has been charged after he was allegedly found in possession of documents designed to facilitate a terrorist attack, police said.

Australian Federal Police deputy commissioner Michael Phelan alleged the documents mentioned "potential government targets" in Sydney.

A second man, aged 21, has been charged with breaching a control order and both men will appear in a Sydney court on Wednesday.

The arrests comes a week after an armed men held 17 people hostage in a Martin Place cafe in Sydney. Three people were shot dead in the siege, including the gunman.

On Tuesday, Australian Prime Minister Tony Abbott said there had been a "heightened level of terror chatter" in the wake of the Martin Place siege and in the lead up to Christmas.

"As you'll all understand, at this level, an attack is likely, 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, and that's why it's important that as well as being reassured that people are aware of the reality of these times," Abbott said.

In September, 800 police officers launched raids across Sydney in the largest counter-terrorism raid in Australia's history.