Counter-terrorism police in Australia have stopped a suspected plot to bring down an aeroplane, Prime Minister Malcolm Turnbull has said.
He was speaking after four people were arrested in raids across Sydney.
Investigators said they had seized materials in the raids that could have been used to make an improvised explosive device.
Mr Turnbull said the raids had been a “major joint counter-terrorism operation”.
He said extra security was in place at domestic and international airports.
Police said it was an Islamist-inspired plot, but they did not link the plan to a specific terrorist group.
Australian Federal Police Commissioner Andrew Colvin said officers became aware people in Sydney were allegedly planning to carry out a terrorist attack using an “improvised device.”
Turnbull said it was an elaborate conspiracy that involved bringing down an airplane.
The suspects were rounded up in raids in four Sydney suburbs, Australian Federal Police and the New South Wales Police Force said in a news release.
The investigation is ongoing, officials said. Police did not specify the date or location of the threat to Australia’s aviation industry.
The suspects are in police custody but have not yet been charged, Colvin said.
Last month, ISIS claimed responsibility for an attack at a suburban Melbourne apartment building where one man was killed and three police officers were wounded.