Despite repeated arrests to dismantle the largest terror cell seen in Sydney, police have warned that offshoots and members in prison pose a continuing threat in an investigation that will "never close".

The close-knit group of extremists at the heart of Operation Appleby first came to the public's attention when 870 police swooped on 27 homes in September 2014.

The raid resulted in two arrests – Ahmad Rahmany, for possessing ammunition, and Omarjan Azari, for allegedly taking an order via phone to kill a random person – and questions soon emerged about whether the operation was overkill.

However, the arrest of 20-year-old Milad Atai on Tuesday brought the number of Appleby arrests now before the courts to 14, which is seen by police as a vindication of the disruptive and pre-emptive strategy first adopted in 2014.