Properties in Middlesbrough are being searched by police after a young man was arrested on suspicion of a terrorism offence.
The 21-year-old, from Middlesbrough, is currently in custody after being arrested in North London on Saturday 30 August.
He was arrested on suspicion of being involved in the commission, preparation or instigation of acts of terrorism contrary to Section 41 of the Terrorism Act 2000.
Four properties - one in North London, two in central Middlesbrough and one in Teesville - have been searched by counter terrorism police as part of the investigation.
Searches are still ongoing at the Teesville property and one of the Middlesbrough addresses.
The investigation, led by Counter Terrorism Policing North East, is being supported by Cleveland Police and Counter Terrorism Command.
Chief Superintendent Dave Sutherland, of Cleveland Police, said: "I know that the nature of this police activity will be concerning to residents in our local communities, and I want to reassure people that public safety is our main priority.
"You will see increased patrols from our neighbourhood teams and I would ask anyone with concerns to speak to these officers.
"The activity is intelligence led and pre-planned and we are working closely with our colleagues from Counter Terrorism Policing North East.
"Our aim is to keep people as updated and informed as we are able to given the sensitive nature of this investigation.
"We appreciate the public's patience and understanding while we carry out this work."