Reuters Australian police officers and forensic experts are seen at a house in the suburb of Glenroy in Melbourne, which was raided in connection to planned terror attacks WATCH the video (5:15)
Australian police arrested four men linked to a Somali militant group, accusing them of planning a suicide attack on an army base and raising concerns al Qaeda-linked militants were seeking targets outside Africa.
The four were arrested in dawn raids on 19 properties across the southern city of Melbourne, after a seven-month investigation involving three police forces and Australia's national security agency ASIO.
Officials said Australia's terrorism warning alert would remain at medium level, where it has been since 2003, but Prime Minister Kevin Rudd said the arrests showed threats remained.
"The sobering element to emerge from today's development is the reminder to all Australians that the threat of terrorism is alive and well," he said in Cairns.
It is the latest high-profile terrorism case that Australian police and intelligence agencies have uncovered.
Australia's biggest terrorism trial ended in February when Muslim cleric Abdul Nacer Benbrika was jailed for 15 years for leading a cell that had planned to bomb a 2005 football match in Melbourne. Altogether, 12 people were jailed over the plot.
In the latest case, the four men arrested were aged between 22 and 26 and were all Australian citizens with Somali and Lebanese backgrounds.
Police said they were linked to the al Shabaab militant group.
One man, Nayaf El Sayed, 25, was officially charged with conspiring to plan or prepare a terrorist act. Police were granted extra time to question three others, Saney Aweys, Yacqub Khayre and Abdirahman Ahmed.
Sayed did not enter a plea or apply for bail, and he refused to stand for the magistrate before he was remanded in jail to reapppear in court on October 26.
"He believes he should not stand for any man except God," his counsel told the hearing.
A fifth man, in custody on other matters, was also being questioned and police have not ruled out more arrests.
Prosecutors told the Melbourne Magistrate's Court they had evidence some of the men had taken part in training in Somalia and at least one had engaged in frontline fighting in Somalia.
They said police had evidence of phone conversations, text messages and surveillance footage, including footage of one of the suspects outside the Holsworthy army base in suburban Sydney.
The court heard the men planned to seek a fatwa, or religious ruling, to support an attack on the Holsworthy army base.
North Africa militants
While Australia has never suffered a peacetime attack on home soil, 95 Australians have been killed in bomb attacks in Indonesia since 2002.
Al Shabaab is a hard-line militant Islamist youth group that is deeply involved in violence in war-torn Somalia. It has vowed to rule the majority Muslim nation by a hard-line interpretation of Islamic law, and has dug up Sufi graves, forced women to wear veils, closed down movie halls and cut off limbs for theft.
Analysts say al Shabaab, which is on the US State Department's terrorism list, is affiliated with Osama bin Laden's al Qaeda network, and has recently had success recruiting from the Somali diaspora and other Muslim youths abroad.
Strategic analyst Carl Ungerer said the Australian arrests point to growing militant activity from North Africa, and proved Australia was still a prime target for militants.
"The arrests this morning clearly show that Australia remains a gold-medal target for international terrorism," Ungerer, from the Australian Strategic Policy Institute, said.
"It is clearly the case, and security intelligence agencies have believed for some time now, there is a real, increasing tempo of al Qaeda activity across all of North Africa, not just the horn," Ungerer said.
"There is a growing concern that the next generation of terrorism is going to be North African."
Acting Australian Federal Police Commissioner Tony Negus told reporters those arrested had planned to storm a suburban Sydney military base with automatic weapons and kill those inside.
"The men's intention was to actually go into the army barracks and to kill as many soldiers as they could until they themselves were killed," he said.
Police said they had worked with international agencies over the raids, but declined to say who tipped them off.
Australia has gradually tightened anti-terrorism laws since the September 11, 2001, attacks on the United States and has more than 1,000 military personnel in Iraq and Afghanistan.
Under Australian anti-terror laws, authorities can detain a suspect for a prolonged period of time without charge, with court approval, while they investigate a case.
Rudd said the arrests were not linked to deadly bombings at two luxury hotels in Jakarta last month that killed three Australians.
Melbourne CBD
Australian Federal Police have caught four people suspected of plotting a terrorist attack in Melbourne. The suspects, all Australian citizens of Somali and Lebanese descent, were arrested early this morning Melbourne time.

"Police believe members of a Melbourne-based group have been undertaking planning to carry out a terrorist attack in Australia and allegedly involved in hostilities in Somalia," a police statement says.

"The men's intention was to actually go into the Army barracks and to kill as many soldiers as they could before they themselves were killed," acting Australian Federal Police deputy commissioner  Tony Negus told a press conference. "This operation has disrupted an alleged terrorist attack that could have claimed many lives."

The raids were carried out by officers from Australian Security Intelligence Organisation, Australian Federal Police, Victoria Police, New South Wales Police and the New South Wales Crime Commission.