Police say they have foiled a mission by Islamic terrorists to launch a suicide shoot-out on a military base in what they say would have been the worst terrorist attack on Australian soil.

Police also say they have pinpointed an Australian terrorist cell supporting and directly involved in insurgency activity in the African country of Somalia.

In seven months of surveillance and a series of raids early today, codenamed Operation Neath, approximately 400 officers from the Australian Federal Police, Victoria Police and NSW Police made four arrests and are questioning several other people.

 

Terror 'a global struggle'

Terrorism expert Professor Greg Barton says that this morning's raids most likely targeted people involved in a global struggle.

The four arrested are all Australian citizens, police say. They are being interviewed and several others are assisting with inquiries, a joint press release said.

A NSW Police spokesperson said 20 officers from the Counter Terrorism and Special Tactics Command helped in the Melbourne phase of the investigation over a number of months.

No raids or arrests were made in NSW, a federal police spokesman said.

"Police will allege that the men were planning to carry out a suicide terrorist attack on a defence establishment within Australia involving an armed assault with automatic weapons," he said.

"Details of the planning indicate the alleged offenders were prepared to complete a sustained attack on military personnel until they themselves were killed."

The alleged plotters had links to groups affiliated with the Al Shabaab terrorist organisation in Somalia - some were of Somali descent, others Lebanese, Mr Negus said.

The investigation revealed some of the alleged plotters had travelled to Somalia to join in fighting there, he said.

'Fatwa sought for terrorism'
 
The group had been "actively seeking a fatwa, or religious ruling, to justify its plan for a terrorist act in Australia," Mr Negus said.

Victoria Police Chief Commissioner Simon Overland said search warrants issued across Melbourne and at Colac in the state's south-west may take 24 hours to complete.

Mr Overland said police had been anxious to control the alleged threat during their investigation and the time had come to act.

"I think it’s sufficient to say that we got to a point where we were satisfied it was appropriate to take some action, and that’s what we did," Mr Overland said.

Mr Overland stressed the overwhelming number of Islamic people in Australia and Melbourne were valued members of the community, not terrorists.

He didn’t rule out further arrests in association with the raids, but said no-one had been apprehended overseas.

Mr Overland said the suspects had conducted reconnaissance at the Holsworthy army barracks in outer south-western Sydney.

There had also been "‘suspicious activity around other bases’’ which he was not prepared to identify.

Leak to newspaper

Mr Overland said he was "extremely disappointed" by leaks that lead to reporting of the raids in The Australian newspaper.

"We will be vigorously pursuing the leak from my end and I expect that the federal authorities will be doing the same,'' Mr Overland said.

Copies of the newspaper were publicly available at 1.30am in Melbourne, well ahead of the raids, he said.

"This, in my view, represents an unacceptable risk to the operation, an unacceptable risk to my staff,'' Mr Overland said.

"It's a risk that I take extremely seriously and is cause for great concern.''

Early-morning raids across city

Victoria Police and the Australian Federal Police executed 19 search warrants at homes in Glenroy, Carlton, Meadow Heights, Roxburgh Park, Broadmeadows, Westmeadows, Preston, Epping and Colac about 4.30am.

Police have set up a crime scene at the corner of View and Glen streets, Glenroy, in Melbourne's north.

Police have blocked off View Street in both directions. Investigators are loading equipment into the house, while they wait for the arrival of forensic chemists.

A small pale green weatherboard house, three doors along from the corner of Glen Street, was among those raided.

Local resident Kylie Bitnell, who has lived in Glenroy for 18 years, described the morning’s events as “a bit scary”.

“You hear about it, but you don’t think it’s going to happen (in your neighbourhood).”