SYDNEY, Australia — The Australian authorities tightened security at airports across the country on Sunday after disrupting what they described as an elaborate plan to detonate a bomb on a plane.
“We believe it’s Islamic-inspired terrorism,” the federal police commissioner, Andrew Colvin, said at a news conference. “Exactly what is behind this is something we need to investigate fully.”
Officials offered few details about the alleged plot, which they described as credible and organized. The police said four men had been arrested in raids at five locations in the Sydney suburbs on Saturday night. It was not clear how or if they knew each other, or whether they were linked to international terrorist groups.
“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,” Mr. Keenan said. “In light of this information, it’s very important that everyone in Australia remains vigilant.”
The raids were carried out by the Australian Federal Police, the New South Wales state police and the Australian Security Intelligence Organization, the country’s main domestic intelligence agency.
Mr. Colvin said little was known about the plot’s specifics, including the location and timing of the potential attack.
“The operation is continuing,” Prime Minister Malcolm Turnbull said, adding that domestic and international travelers in Australia should expect extra scrutiny at airports.
The additional security measures — “some of the measures will be obvious to the public, some will not be,” Mr. Turnbull said — come as Australia is in the midst of a security overhaul that involves unifying counterterrorism, intelligence and immigration and border enforcement under a single government minister, Peter Dutton.
Mr. Turnbull said people should be vigilant but not afraid.
“The threat of terrorism is very real,” he said, while adding that “those traveling should go about their business with confidence.”