Police said they are not able to reveal the nature of a suspected terror plot after arrests were made in Sheffield.
Anti-terror police swooped to arrest a man at a block of flats in Kelham Island on Thursday evening. They also carried out an operation in Huddersfield.
The men, aged 24, and 29, are both from Huddersfield and were arrested on suspicion of offences under Section 5 of the Terrorism Act.
The North East Counter Terrorism Unit, which led the operation, said they cannot comment on the nature of any suspected plot.
But the laws under which they were arrested relate to a person intending to commit "acts of terrorism, or assisting another to commit such acts."
Suspects found guilty of these offences face life in prison.
An NECTU spokesperson said officers were acting on "recently received intelligence" but the arrests are not connected to the recent terror attack in Manchester.
They added: "We are unable to give any further detail and will not confirm or respond to speculation regarding the nature of any potential offences."
The two men remained in custody today and were being questioned by specialist officers.
In addition a third man, aged 23, was arrested in Sheffield this morning on suspicion of assisting an offender.
The NECTU spokesperson said the investigation was supported by both South Yorkshire and West Yorkshire Police and added: "Both property searches have now concluded and we would like to thank the local communities for their patience and understanding."
Nick Meeks, aged 27, was working at his apartment on Cornish Street when armed officers stormed the block of flats at around 5pm.
He said: "I was sat there working on my laptop and there was a huge bang. I've never heard anything like it.
"Naturally I popped my head out of the door and there was smoke billowing down the corridor and police in full armed gear pointing guns down the corridor shouting at me to get back inside my flat. You do what you're told when there's a gun in your face."
The NECTU spokesperson said: "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."