Australia's Prime Minister has confirmed that police have disrupted what they believe was a terrorist threat to bring down a plane.
A large-scale security operation is under way in Sydney where four men have been arrested.
Additional security has been put in place at all domestic and international airports in Australia.
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Prime Minister Malcom Turnball says police have raided several addresses and made substantial seizures:
Mick Fuller is the police commissioner for New South Wales. He says they are not taking any chances: