Police raided three homes in Sheffield this morning as part of a counter terrorism operation, with an address in Shirebrook Road, Meersbrook, one of those searched.
Residents claim they heard an explosion at 5.30am, which is now believed to have been police officers entering the house.
The three raids in Sheffield, and one in Chesterfield, are said to have been 'intelligence led' and 'pre-planned'.
It is believed they were carried out simultaneously.
Four men were arrested in total - three, aged 22, 36 and 41 in Sheffield and one, aged 31, in Chesterfield.
They are all being held on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism under section 41 of the Terrorism Act 2000.
They have been taken to a police station in West Yorkshire for questioning.
Today's operation was carried out by the North East Counter Terrorism Unit.
A spokesman said: "We recognise that local people may have concerns as a result of this activity.
"We would ask people to remain alert but not alarmed and we are grateful for the assistance and understanding of people locally.
"Residents will be kept as informed as possible and we are grateful for their understanding, patience and support while these enquiries continue."