Two men were arrested on Wednesday during a counter-terrorism operation in Sydney, with a key Australian naval base among locations they were allegedly targeting, police said.

Their detention comes just weeks after five people were held over a plot aimed at an Australian government building.

The Islamic State group is working to boost its presence in Indonesia with dreams of creating a "distant caliphate" in the world's most populous Muslim-majority country, Australia warned on Tuesday.

Attorney-General George Brandis, who spent Monday in meetings between Indonesian and Australian ministers, police chiefs and security officials, said it constituted a threat to Australian and Western interests.

Up to 15 homes have been destroyed by bushfires near Melbourne but cooler conditions Monday aided crews battling them to get the upper hand, officials said.

A number of blazes ignited over the weekend, whipped up by strong winds and searing heat, and they quickly ran out of control.

Australia's spy chief has told politicians from the ruling conservative party to tone down their criticism of Islam as it could pose a national security risk, according to reports.

Debate over anti-Muslim rhetoric in Australia has spiked after ousted prime minister Tony Abbott last week wrote in a newspaper column that "we can't remain in denial about the massive problem with Islam".

An Australian military surveillance plane has flown near disputed areas of the South China Sea, it emerged Wednesday, with the crew heard warning China's navy it was on a freedom of navigation mission.

Tensions in the region have mounted since China transformed reefs in the South China Sea into small islands capable of supporting military facilities, a move the United States says threatens free passage in an area through which one-third of the world's oil passes.

Two people, including a 15-year-old boy, were arrested Thursday in Sydney over a terror plot targeting a government building, with authorities expressing alarm at the age of those being radicalized.

The teenager and 20-year-old man were seized at their homes and charged with one count each of conspiracy to conduct an act in preparation for a terrorist act.

Deposed Australian prime minister Tony Abbott declared Wednesday "cultures are not all equal" and the West should proclaim its superiority over Islam, sparking accusations he is trying to "Trumpify" the nation's politics.

The staunch Catholic also called on Australians to stop apologizing for their values.

An Australian who joined Kurds battling the Islamic State group in Syria arrived back home Monday with his parents pleading with authorities not to charge him under foreign fighter laws, calling him "a hero".

Ashley Dyball, 23, was detained in Germany while taking a break from a Kurdish military campaign against IS in northern Syria and deported on Saturday night.

An Australian man who reportedly joined a group fighting Islamic State jihadists in Syria will be deported from Germany, the foreign ministry said Saturday.

Australian media had reported that Ashley Dyball was detained in Germany after traveling to Europe for a break from working with a Kurdish militia group known as YPG.

Australia's parliament has passed legislation to strip dual nationals of their citizenship if they are convicted of terrorism offenses or found to have fought with banned groups overseas, despite concerns about deporting jihadists.

Attorney-General George Brandis said the Australian Citizenship Amendment (Allegiance to Australia) Bill, passed late Thursday, updated existing law to reflect "the new age of terrorism".