Terrorism officers have arrested two men in Sheffield and Huddersfield as part of an ongoing operation.
Dozens of armed officers flooded Kelham Island earlier this evening. Loud bangs were heard by residents as units entered a flat to detain a man.
Officer from the North East Counter Terrorism Unit said the raids were not linked to the Manchester terror attack and were acted upon 'recently received intelligence'.
One witness said counter terrorism police appeared to be raiding a flat in Kelham Island this afternoon, at around 5.30pm.
A spokesman said: "Officers have today arrested two men from Huddersfield on suspicion of offences under Section 5 of the Terrorism Act.
"The men, age 24 and 29, were arrested at separate locations in Huddersfield and Sheffield
"Searches are being carried out in properties in Huddersfield and Sheffield.
"There are no connections to the recent incident and investigation in Manchester.
"The operation is based on recently received intelligence.
"We understand that people may have concerns as a result of this activity and we are grateful for the patience and understanding of the public while these enquiries are carried out.
"The public may have heard loud bangs at the time that police entered the property. We would like to reassurance you that this was part of the method of entry to gain access to the property."