A 23-year-old man was arrested in the early hours of this morning as part of the investigation into the Manchester bombing.
A scene guard remains outside a property in Brunswick Road, Shoreham.
Twenty two people died and scores more were injured when Salman Abedi, 22, blew himself up after an Ariana Grande concert at the Manchester Arena.
Sussex Police said: “Early on Monday (29 May) officers investigating the attack on the Manchester Arena arrested a 23-year-old man in Shoreham on suspicion of offences contrary to the Terrorism Act.
“A scene guard remains in place at the address where the man was arrested.
“Today’s action is part of an ongoing investigation by Counter Terrorism Policing North West, working together with Sussex Police. This phase of the operation is still in its infancy so the information we can release is limited.”
Assistant Chief Constable Steve Barry, of Sussex Police, said: “I understand that this kind of activity can cause concern for people living in nearby communities and would like to thank them for their understanding and patience.
“As a result of today’s operation, Sussex Police is working very closely with community groups, community leaders, partner agencies and individuals to make sure concerns are addressed and that we provide the best possible service to local people.
“Over the coming days and weeks we will be continuing to work with our local communities to address any concerns they may have.
“We always need the public’s help to defeat terrorism by being extra vigilant and letting us know of any suspicious behaviour or activity.”
“Terrorists want to create discord in our communities but Sussex has a long history of our communities living and working together.
“We will continue to work closely with our communities by carrying out patrols over the coming weeks and addressing any concerns they may have.
“Public safety is the paramount concern for the police and will continue to be our top priority and we have a duty to act and protect the public.
“I’d ask local communities to stay alert, but not alarmed, be extra vigilant and to report any suspicious behaviour to the anti-terror hotline on 0800 789321 or in an emergency call 999.”