Australian Prime Minister Malcolm Turnbull today said that anti-terror raids carried out in Sydney yesterday "disrupted" an alleged plot to bring down an
aircraft, even as four people were held in this connection.

According to media reports yesterday, four men were arrested during anti-terror raids carried out by Australian federal police, New South Wales police at five
properties in Sydney.
 
"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," Turnbull
said.
  
Police allege the group of Sydney men were planning to use an "improvised device" to carry 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.

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 yesterday.
  
Turnbull said the "major counter-terrorism operation" was underway and extra security measures had been put in place at major airports.

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