The four, all Australian citizens with Somali and Lebanese backgrounds, were arrested in dawn raids on 19 properties across Melbourne, after a seven-month investigation involving several forces and Australia's national security agency ASIO.
The group in question is al Shabaab, which is conducting an international recruitment campaign backed by al Qaeda's propaganda network for fighters to join its push to take power in Mogadishu and impose strict Islamic rule.
Although al Shabaab plays up its link to the transnational network of Osama bin laden, attacking Western targets overseas is not its primary goal, which is overwhelmingly domestic.
But one consequence of its use of ethnic Somalis from the millions-strong diaspora community may be that veterans head home with the funds or skills to attack Western targets of their own volition, Western counter-terrorism officials say.
"The chances are extremely remote that this was Shabaab saying 'Go off and strike Australia'," said Will Hartley, Editor of Jane's Terrorism and Insurgency Center, a security consultancy and information provider.
"NOT MERELY RESISTANCE FIGHTERS"
"Far more likely is that Australia was targeted by Australians who had been in Somalia, were radicalized, and were intent on carrying out or expanding the jihad themselves ... not under Shabaab orders," he said.
The arrests coincide with a surge in Western concern about radicalization of some Western converts to Islam. On July 29 U.S. Attorney General Eric Holder warned of increased "radicalization" of Americans going abroad and then returning home with the "aim of doing harm to the American people."
He was speaking two days after seven people were arrested in North Carolina for allegedly plotting attacks overseas. Holder also expressed concerns about a group of young Somali men leaving the Minneapolis area to join al Shabaab.
Acting Australian Federal Police Commissioner Tony Negus said those arrested on Tuesday had planned to storm a suburban Sydney army base with automatic weapons and kill those inside.
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.
Western officials worry that today's chaotic Somalia resembles Afghanistan in the 1990s, when militants including bin Laden's associates used the safe haven of ungoverned areas on the Pakistan border to plan attacks on Western targets.
In a speech posted on militant web forums on July 30, an al Qaeda leader, Abu Yahya al-Libi, appeared to urge Somali supporters of Shabaab to widen their list of targets beyond the nationalist agenda of ending foreign occupation - a reference to African Union peacekeepers in Somalia.
"You and we are mujahideen in the Cause of Allah, fighters against the enemies of Allah. We are not merely resistance fighters who push out enemies who came to our lands," he said, according to a translation by the Site Intelligence Group. He added: "We fight to drive out the foreign occupation from our lands ... and to eliminate every regime or law that disagrees with our faith, and so that Islam alone rules our lands and so that all mankind are servants of Allah alone."
Rashid Abdi, a Somalia expert at the International Crisis Group, said al Qaeda's internationalist rhetoric in support of al Shabaab on militant chatrooms and Web sites had helped widen the group's appeal among radical communities around the world.
And al Shabaab's own propaganda has drawn parallels between itself and the Taliban in Afghanistan and insurgencies in Algeria and Chechnya, in an apparent attempt to attract hardcore militants elsewhere in the world to join its fight.
AL QAEDA ORBIT
But domestic Somali politics was also a driver in al Shabaab's "moving into the al Qaeda orbit," Abdi said.
Al Shabaab, which holds swathes of south and central Somalia, has been enraged by Western and African backing for a new government formed this year and feels it would already have defeated the administration if it had not been for this support.
The United States has offered military support to Somalia's government, including more than 40 tons of weapons and ammunition, to help it fight insurgents, a senior U.S. official has said. It has also offered training for security forces.
Shabaab's radicalization "is a function of what is going on militarily and politically on the ground," Abdi said.
"They feel besieged, they feel that their victory has been snatched from them largely because of Western interference... You can see why the west is now more of a target for al Shabaab."
(Editing by Janet McBride)