Australian police have arrested four people in the southern city of Melbourne after uncovering an alleged plot to attack an army base. The suspects were detained after raids involving hundreds of police officers.
Australian police have said they have uncovered a plan for suicide attackers to target a military base.
More than 400 officers have taken part in one of the country's biggest counter-terrorism operations. They searched 19 properties across Melbourne in pre-dawn raids Tuesday.
The four suspects are Australian citizens of Somali and Lebanese descent, and are aged between 22 and 26.
Investigators think the men had links with Somalia's al-Shebab group, which is fighting a deadly insurgency against that country's government.
The police allege that some of the suspects arrested in Melbourne had traveled to Somalia to take part in the fighting.
Tony Negus, acting chief commissioner of the Australian Federal Police, says the arrest follow an exhaustive investigation stretching back for seven months.
"This investigation has been a massive physical and electronic surveillance operation over that time," Negus said. "Police will allege that the men were planning to carry out a suicide terrorist attack on a defense establishment within Australia involving an armed assault with automatic weapons."
Al-Shahab is linked with the al-Qaida terrorist network. U.S. and Somali officials say the group wants to install an ultra-conservative Islamic government in Somalia.
News of the arrests follows an admission last week by an Australian Islamic convert, Shane Kent, to plotting to kill thousands of people in an attack on a sports event in Melbourne.
Eight members of the same radical cell have already been jailed over plans to bomb the 2005 Australian Football League Grand Final, which attracted a crowd of 92,000.
Australia has never suffered a terrorist attack on its soil. Critics of Canberra's decision to send troops to the wars in Iraq and Afghanistan argue the deployment has made the country more of a target for extremists.
The Australian government rejects that argument, saying that success in those conflicts will ultimately make the country safer.