A 46-year-old man has been arrested on suspicion of a terrorism offence.
Counter-terror officers raided a property in the Lincolnshire area early on Friday and detained the man on suspicion of membership of a proscribed organisation and malicious communications.
He remains in police custody for questioning and inquiries are ongoing.
Detective Chief Superintendent Dominic Scally, head of counter terrorism policing for the North West, said: "Today's arrest forms part of a wider operation into the activities of a proscribed organisation.
"The man remains in custody to be questioned by specialist officers and our investigation continues.
"Those involved in proscribed organisations have a detrimental effect on the communities others work so hard to build, so it is essential people contact us with information so we can put a stop to those who support extremist ideologies.
"Any information that people have can be dealt with in the strictest of confidence by calling the police on 0800 789 321."