Australian police have foiled what they claim was an ‘Islamic-inspired’ terror plot designed to bring down an aeroplane with a home made bomb.

Prime Minister Malcolm Turnbull confirmed raids carried out in the New South Wales state capital of Sydney on Sunday “disrupted” what he called an “elaborate” conspiracy. Extra security is now in place at airports around the country as a result.

Four men were arrested after the raids at five properties in the Sydney inner-city suburb of Surry Hills, and the outer lying suburbs of Lakemba, Wiley Park and Punchbowl.

It is understood the alleged cell was capable of making an improvised explosive device, but sources told ABC News it is unclear whether they would have succeeded in getting it onto a plane.

“We do believe it is Islamic-inspired terrorism. Exactly what is behind this is something that we will need to investigate fully,” Australian Federal Police (AFP commissioner Andrew Colvin said.

He then outlined the police work that went into the arrests.

“In recent days, law enforcement has become aware of information that suggested some people in Sydney were planning to commit a terrorist attack using an IED (improvised explosive device),” he told a news conference.

He said police did not yet have information on “the specific attack, the location, date or time”, adding that he expected the investigation to be “long and protracted”.

Authorities received information about the alleged plot on Wednesday and beefed up security at Sydney Airport on Thursday. The NSW joint counter-terrorism team then decided to move ahead with raids late on Saturday evening.

All four men are being held at the Sydney Police Centre in Surry Hills. The suspects can be held without charge for around a week.

Since 2014, 70 people have been charged as a result of 31 counter-terrorism operations around Australia.

Australia’s terror threat level remains at probable.