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.
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David John Woods and Leslie Peter Baines are said to have carried out “a savage and brutal attack” on Matthew Cassidy, in May last year.
The man is said to have approached the 11-year-old riding on his bike and offer him a lift home.
It is believed weapons, including possibly a small axe, were used in the street fight in the Llanrumney area of Cardiff.