Police have arrested five people in a series of raids in connection with the terror-linked killing of a civilian police worker.

New South Wales police say more than 200 officers swooped into homes in western Sydney on Wednesday and arrested the men as part of their investigation into the killing of Curtis Cheng. Cheng was a police finance worker who was shot by an Iranian teenager while leaving work in the western Sydney suburb of Parramatta last week. The killer was shot dead by police.

Police said on Saturday that they believe the killing was politically motivated and therefore linked to terrorism. But they said the teen's specific motivations were unclear.