A bomb disposal squad has been sent to one of the properties raided by anti-terror cops in Sheffield this morning.
The Royal Logistics Bomb Disposal Team arrived at about 5pm outside the Fatima Community Centre in Brunswick Road, Burngreave, which has been cordoned off by police.
The squad are understood to have earlier carried out a controlled explosion during a counter terrorism raid in Chesterfield.
The North East Counter Terrorism Policing Unit has raided four properties in Sheffield today - two in Burngreave, one in Stocksbridge and one in Meersbrook. A search warrant was also executed at a property in Chesterfield.
A search of the property in Stocksbridge has concluded while work is continuing at the other sites.
Three men, aged 22, 36 and 41, arrested in Sheffield and a 31-year-old man arrested in Chesterfield remain in custody.
All four were arrested 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 West Yorkshire for questioning.
A spokesman for the North East Counter Terrorism Policing Unit said the raids were 'intelligence led' and 'pre-planned'.