Over the weekend, four men were taken into custody by police in a series of raids in the suburbs of Sydney. "The disrupted plot -- the details of which are still developing -- serves as a reminder that while recent attacks in Australia have tended toward low-skilled attacks using basic weapons, ISIS-inspired extremists have not abandoned more sophisticated plots, such as those involving aviation", the State Department notice said.
A 50-year-old man was released on Tuesday night, the Australian Federal Police (AFP) said in a statement, adding that no criminal charges had been filed against him.
"This investigation remains ongoing, and further information will be provided at an appropriate time".
Two other USA officials, also speaking on condition of anonymity, said communications between the alleged plotters in Sydney and members of Islamic State in Syria were intercepted by a foreign intelligence service.
"Etihad is complying fully with the enhanced security measures at airports in Australia and monitoring the situation closely".
In an earlier statement, Etihad Airways had urged its passengers travelling to Australia to arrive at the airport early in light of the new security measures. "Safety is the airline's number one priority". The airline has built strong ties to the country, buying a stake in alliance partner Virgin Australia, featuring down-under stars including Nicole Kidman in advertising campaigns and sponsoring Melbourne's soccer team and its home stadium.
Cops believe the two Lebanese-Australian father-and-son duos schemed to stuff explosive material inside the culinary gear then take it on a flight from Sydney to the Middle East, the Daily Telegraph reports.
Etihad's hub in Abu Dhabi is 130 kilometers (80 miles) from Dubai's main airport, the world's busiest for global flights.
"These networks, whether they're familial or otherwise, are very important", said Jacinta Carroll, head of the Australian Strategic Policy Institute's Counter Terrorism Policy Centre. But it did not say whether it is involved in the investigation. Two other men are also being held and none have been charged.
The US officials declined to identify the service and United Kingdom officials refused to confirm or deny playing a role in detecting the plot.