5 arrested for planning to leave Australia by boat to join ISIS

Australian police have arrested five men, including a top hardline Islamic preacher, who were planning to join the dreaded IS terror group by sailing to Indonesia by a boat.

The arrests took place in Queensland on Tuesday as the men with cancelled passports were towing a boat towards Cape York, in far north Queensland.

The men included Islamic preacher Musa Cerantonio, Shayden Thorne, the brother of another hardline Islamist, Junaid Thorne, police said.

Cerantonio was deported in 2014 from the Philippines where he had been hiding. At that time he was regarded as one of the world's most prominent online English-language preachers of the extremism espoused by the Islamic State.

They have been held on suspicion of foreign incursion offences, media reports said.

"The men had been under investigation for a number of weeks. The men, aged between 21 and 33, have not yet been charged. They were in a boat that was seven-metres long," Australian Federal Police Deputy Commissioner Neil Gaughan said.

"The fact that they had travelled from Melbourne to far north Queensland indicates that these people were extremely committed in their adventure and their attempt to leave the country," he added.

"The suspicion is that they were seeking to leave Australia by vessel to avoid the fact that they could not travel by air because their passports had been cancelled," he said.

Victoria Police Deputy Commissioner Shane Patton said police would be considering charges after the men were questioned.

"We have a requirement to ensure that people can't get offshore to go and fight in other countries, can't get offshore to become hardened terrorists and come back here and pose a risk," he said.

"If disruption means ultimately we don't get sufficient evidence so we can charge them, we'll accept that risk," he said.

Federal Attorney-General George Brandis confirmed the arrests and said it demonstrate the threat to Australians from those engaging in acts of terrorism, including acts of terrorism in foreign countries, remains real and present.

"I want to emphasise that the offences on suspicion of which these five men were arrested were not to conduct an act of terrorism on the Australian mainland but to travel, in breach of Australian law, overseas to engage in foreign incursion against the Australian criminal code," Brandis said.

"Nevertheless, the Australian government takes very seriously, whether it be acts of domestic terrorism or threats to commit acts of domestic terrorism, or attempts by Australians to travel overseas to engage in terrorist war fighting on foreign soil, in this case, as I said before, in Syria," he added.