CANBERRA, Australia — Security remained heightened in airports around Australia with more intense screening of luggage after law enforcement officials thwarted what a ****** chief described on Monday as a “credible attempt to ****** an aircraft.”

Prime Minister Malcolm Turnbull and Border Protection Minister Peter Dutton declined to comment on newspaper reports that Islamist extremists planned to **** the occupants of a plane with ****** gas and that a homemade **** was to be disguised as a kitchen mincer.

“****** will allege they had the intent and were developing the capability,” Turnbull told Australian Broadcasting Corp.

Turnbull announced on Sunday that “a ********* plot to bring down an airplane” had been disrupted, but revealed few details.

Four men arrested in raids in Sydney late Saturday – two Lebanese-Australian fathers and their sons – had yet to be charged.

Australian Federal ****** Commissioner Andrew Colvin said a court ruled Monday that the four could be detained without charge for seven days from their ****** under counterterrorism laws.

“We believe we have disrupted a legitimate and credible attempt to ****** an aircraft,” Colvin told reporters without elaborating.

Colvin has repeatedly described the ****** as a “device,” without mentioning whether it was *********.

“The plot that we are investigating we believe was an attempt to put a device onto an aircraft, but beyond that the speculation is just that _ speculation,” he said, adding that ****** had “many working theories.”

Colvin and the government will not comment on media reports that the suspects were not previously known to Australian security officials and that their arrests followed a tip from a foreign intelligence agency.

“Australians can be assured that we have very fine intelligence services and we moved extremely quickly on this one and, as you can see, with the right outcomes,” Turnbull said.

The Australian newspaper cited multiple anonymous sources saying that the plotters were constructing a “non-traditional” ********* device that could have emitted a toxic, sulfur-based gas to **** or immobilize everyone on the aircraft.

Sydney’s The Daily Telegraph newspaper reported that the plotters planned to make a **** from wood shavings and ********* material inside a piece of kitchen equipment such as a mincing machine.

****** raided five homes Saturday and removed a domestic grinder and a mincer used to make sausage, the newspaper said.

The plot involved smuggling the device onto a flight from Sydney to the ***********, possibly Dubai, as carry-on luggage, the newspaper said.

Fairfax Media reported that the **** was found in a home in the inner-city suburb of Surry Hills, a few doors from the local mosque.

Turnbull declined to say whether the group was guided by someone overseas.

“It’ll be alleged that that this was an Islamist extremist, ********* motivation,” the prime minister said.

Dutton, the border protection minister, urged travellers to arrive at Australian airports two hours before domestic flights and three hours before international flights to allow time for more screening. Luggage should be kept to a minimum and those accompanying travellers should not enter secured parts of terminals.

He declined to detail the ****** that the security staff were searching for.

“There’ll be lots of speculation around what the intent was … but I don’t want to add to that,” Dutton told Nine Network television. “Our focus now really is making sure that people who are planning a ********* ****** are thwarted.”

Security has been increased at Sydney Airport since Thursday because of the plot and has since been increased in all major Australian international and domestic terminals.

Turnbull would not speculate on how long airport security would remain elevated. “They will be required for as long as the ****** is assessed as requiring them,” he said.

Australia’s ********* ****** level remained unchanged at “probable.”

Australia is a staunch ally of the United States and partner in military campaigns in the ***********. The Islamic State group has highlighted Australia as a Western target.

The plot was the 13th disrupted by ****** since Australia’s ********* ****** level was elevated in 2014. Five plots have been executed.