Police told a news conference that the potential targets of the plot included the headquarters of the Australian Federal Police in Sydney, Australia's largest city, as well as randomly chosen civilians.

The arrests resulted partly from evidence seized during police raids in December 2014, a police statement said.

Three other men, all of them already in custody on terrorism-related offences, were also charged later as part of the same operation.

Each of the men, aged 21, 22 and 22 - had been charged with one count of conspiracy to conduct an act in preparation for a terrorist act, the same charges leveled against the two seized in the raids earlier, police said.

Australia, a staunch ally of the United States and its battle against Islamist militants in Iraq and Syria, has been on heightened alert for attacks by home-grown radicals since last year.

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