The Australian government will introduce tough new legislation in parliament next week to tackle terrorism, news media reports say, in the aftermath of the biggest crackdown in the country's history.

Tony Abbott, Australia's prime minister, will seek sweeping counter-terrorism powers when the proposals go before the house on Wednesday, NewsCorp Australia reported.

Thursday's unprecedented raids in Sydney and Brisbane had foiled a plot by fighters from the Islamic State of Iraq and the Levant (ISIL) group to carry out gruesome "demonstration executions" which could have taken place within days, Abbott said.

Security has also been stepped up in the capital Canberra, and at military bases, airports and sporting events after parliament and government officials had been mentioned as potential targets in "chatter" between extremist networks in the Middle East and Australia.

Fifteen people were arrested when hundreds of police officers raided dozens of homes in Sydney and Brisbane on Thursday, but only one person remained in custody on Saturday, officials said.

Omarjan Azari, 22, was charged with planning a terrorist act that prosecutors said was intended to "shock, horrify and terrify" the community and involved the "random selection of persons to rather gruesomely execute" on camera.

Detention orders

Federal police had for the first time used preventive detention orders to hold three of the 15 without charge, the Australian Broadcasting Corporation reported.

The men were released on Friday.

The orders are designed to counter an imminent threat of attack and can be used to hold people for up to 14 days.

But Abbott says current legislation is inadequate to fight the threats to Australia from groups such as ISIL, which he has described as the nation's greatest national security challenge.

Under the new powers, advocating a terrorist act will become illegal, The Weekend Australian said.

The new offence will carry a maximum five-year jail sentence and make it illegal for an individual to intentionally counsel, promote, encourage or urge a terrorist act, the newspaper said.

Police will also be given powers to secretly search the homes of suspects.

Prosecution risk

The government will further seek powers to proscribe visits to cities or regions where terror groups are active.

People travelling to such areas without a valid reason could face prosecution.

"There's legislation that will shortly come before the Parliament to boost the range of offences," Abbott said  on Thursday without providing details.

"It's not always easy to prove that someone has been engaged in terrorist activity overseas.

"It's often very hard to get witnesses ... so we'll be strengthening offences in this area."

The government believes up to 60 Australians are fighting alongside ISIL fighters, while another 100 are actively working to support the movement at home.

Canberra has committed 600 troops and aircraft to the US-led coalition gearing up to fight the ISIL organisation in Iraq.

Source: Agencies