The yellow "be aware" alert comes into force from 09:00 GMT on Wednesday.
Concern that cases are not being reported prompts Gwent Police to launch Operation Makesafe.
The boy tells a court he downloaded Islamic State material to fuel his hatred towards terrorists.
Dragons are close to beating Scarlets to sign Wales back-row Ross Moriarty who has yet to be offered a new Gloucester deal.
Cardiff return to the Championship's automatic promotion places as Callum Paterson's late goal gives them victory at Barnsley.
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