A man has been arrested on suspicion of making or possessing explosives in an investigation being led by counter-terror officers.
The 25-year-old, from Basingstoke, Hampshire, was detained on Wednesday and was also arrested on suspicion of possessing a firearm without a certificate. He remains in custody.
Counter Terrorism Policing South East are leading the investigation and a property in Penny Black Lane, Basingstoke, is being searched.
Hampshire Police said a number of neighbouring properties have been evacuated while the search takes place although it is believed there is no wider threat to the public at this time.
Chief Inspector Matthew Reeves, district commander for Basingstoke and Deane, said there would be an increased police presence in the area and appealed for calm in the community.
He said: “I understand that this is a worrying time in the local community, thankfully incidents of this nature are relatively rare.
“We are assisting our colleagues at Counter Terrorism Policing South East and our partner agencies to address any concerns you may have.
“You may notice an increased police presence, please don’t be alarmed, officers are involved in the investigation and are there to assist and support. Please approach these officers if you have any concerns or questions.”
He added: “This is an active investigation so please refrain from speculation, I’d like to take this opportunity to thank the community for their support so far with this investigation.”