Australia foils Islamist-inspired terror plot to bring down plane

Australian Prime Minister Malcolm Turnbull said security has been beefed up at all major domestic and international airports following the arrest of four men.

"I can report last night that there has been a major joint counter-terrorism operation to disrupt a terrorist plot to bring down an airplane," he said.

"We face a range of terrorist threats. Some of them are lone actors, who activate very quickly with very little warning.

On other occasions you get quite elaborate conspiracies this appears to be in that category," he added. Earlier, four men were arrested during anti-terror raids carried out by federal police, New South Wales police and ASIO at five properties in Sydney on Saturday.

Police said that they found the material and items that could be used to make a homemade bomb, when they raided the house at Surry Hills on Saturday. Police alleged that the arrested men were planning to use an "improvised device" to carry out an attack to bring down an aircraft but no details on a particular target, location, time or date were uncovered.

Australian Federal Police Commissioner Andrew Colvin said they had no reason to believe airport security had been "compromised" but a heightened state of security has been implemented.

"We do believe it is Islamic-inspired terrorism. Exactly what is behind this is something that we will need to investigate fully," Colvin said.

"We are investigating information indicating the aviation industry was potentially a target of that attack," he added.

Prime Minister Turnbull said those with plans to travel should do so with confidence, but allow extra time for security screening because of the threat.