A group of Islamic extremists who were detained today planned a suicide attack on an Australian army base with the aim of killing as many soldiers as possible, a court was told.

One man has been charged with planning a terrorist act and police have been granted extra time to question another three men arrested this morning in a series of counter-terrorism raids across Melbourne.

About 400 police officers and members of the Australian Security Intelligence Organisation swooped on 19 properties, detaining several men, all Australian citizens of Somali and Lebanese background, in the pre-dawn raids.

A fifth man, in custody on other matters, was also being questioned and police have not ruled out more arrests.

Police allege the group was at an advanced stage of preparing to storm army barracks in Sydney and Melbourne in retaliation for Australia’s military involvement in Afghanistan and Iraq.

Kevin Rudd, the Australian Prime Minister, said the discovery of the plot would not force him to pull troops out of Afghanistan.

He admitted the Afghan operation, which claimed its eleventh Australian life last month, was unpopular but said that it was necessary to cut off militant training opportunities.

"If we're to deal with the threat of terrorism at its various levels we must be dealing with where terrorists are trained," Mr Rudd said.

Members of the hardline group had been observed carrying out surveillance of Holsworthy Barracks in Sydney and of military bases in Victoria. Electronic surveillance also picked up discussions about how to obtain weapons to carry out what would have been the worst terror attack on Australian soil.

"The men’s intention was to get into the army barracks and kill as many as they could," Tony Negus, acting Commissioner of the Australian Federal Police, said. "They were planning to carry out a suicide terror attack. . . a sustained attack on military personnel until they themselves were killed.”

Andrew Scipione, Commissioner of New South Wales Police, said that a terrorist attack on Sydney's Holsworthy Barracks was "likely imminent'' when police carried out the raids.

Melbourne Magistrates' Court heard how, during a seven-month-long investigation dubbed Operation Neath, police had gathered "voluminous" amounts of telephone intercept recording material, including text messages, about the planned attack.

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