Four men have been arrested on suspicion of plotting terror attacks.
Specialist counter terrorism police officers arrested three men, aged 22, 36 and 41, at addresses in Sheffield on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism.
A 31-year-old man was arrested at an address in Chesterfield on suspicion of the same offence.
One of the houses raided was in Shirebrook Road, Sheffield, where locals claim they heard an explosion at around 5.30am.
Residents said officers then arrived at the scene and carried out a search, and the house remains under police guard.
Police confirmed all the properties are currently being searched and the men have been taken to a police station in West Yorkshire for questioning.