Australian counter-terrorism police carried out raids on Saturday in at least three Sydney suburbs as well as the inner city.

"This activity relates to an ongoing investigation," a police spokesman said, without divulging further details.

Australia's national broadcaster ABC said at least one man was arrested during the raids.

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"These operations are designed to disrupt and prevent plans to undertake terrorist attacks in Australia," Prime Minister Malcolm Turnbull said in a statement.

"The public should be assured that our security and intelligence agencies are working relentlessly to keep us safe," the premier added.

Radicalization threat

Australian security officials are said to have prevented at least 12 extremist attacks on home soil since September 2014. Five attacks have taken place, however, including a fatal June shootout in Melbourne that was claimed by the so-called "Islamic State" (IS) group.

Many Australian citizens supportive of Islamist ideology have traveled to the Middle East - including Iraq and Syria - to fight along IS and other militant groups. Their return to Australia is believed to pose a serious security risk.

Read: Australia arrests suspect for advising 'Islamic State' on missile design

Australia is a US ally in Syria and supports groups opposed to President Bashar al-Assad's dictatorial regime.

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shs/rc (AFP, Reuters)