Australian officials say they have arrested four men in connection with a plot to bomb an airplane, following Saturday evening raids. Police say the plot was "Islamic-inspired."
"In recent days, law enforcement has been become aware of information that suggested some people in Sydney were planning to commit a terrorist attack using an improvised device," said Australian Federal Police Commissioner Andrew Colvin, The Associated Press reported.
"We do believe it is Islamic-inspired terrorism," said Colvin. "Exactly what is behind this is something that we will need to investigate fully." He said authorities had few details on the location, date, or time of the attack, but "we're investigating information indicating the aviation industry was potentially a target of that attack."
The plot is reportedly more sophisticated than the lone wolf attacks that have struck Australia before.
"I can report last night that there has been a major joint counterterrorism operation to disrupt a terrorist plot to bring down an airplane," Prime Minister Malcolm Turnbull told reporters, including the AP. "The operation is continuing."
The Sydney Morning Herald described the scene, which yielded four arrests and reportedly the discovery of a homemade bomb: "Bomb squad officers were among dozens of police who raided five properties across Sydney on Saturday evening, smashing their way through glass doors and brick walls." On Sunday, the newspaper said, "Forensic officers in gas masks combed the properties ... and removed bags of evidence."
"[The men] have family links to each other and links to previous plots and established networks," according to the Herald. "Investigators believe that, based on the degree of sophistication of the plot, the group may have had some overseas direction."
Security has been tightened at airports around the country, with travelers advised to allow extra time to get through security and baggage screenings, though some travelers at Sydney Airport said that the airport seemed quieter than usual on Sunday.
"The primary threat to Australia still remains lone actors, but the events overnight remind us that there is still the ability for people to have sophisticated plots and sophisticated attacks still remain a real threat," Justice Minister Michael Keenan said, The New York Times reported. "In light of this information, it's very important that everyone in Australia remains vigilant."
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