An 18-year-old man from Grangetown in Cardiff has been arrested on suspicion of terrorism offences.
South Wales Police say he has been arrested under the Section 5, Terrorism Act 2006 for assisting in the preparation of an act of terrorism.
Police said that today's arrest was not linked to any immediate threat to public safety.
More top news
Conner Marshall, 18, died after a 'vicious and unprovoked attack' in Porthcawl in 2015.
A new campaign is being launched to tackle arson in Wrexham following a number of attacks in the area.
ITV Wales can reveal thousands of patients have waited over an hour for an ambulance since the 'amber' category was introduced last year