South Wales Police say there may be a possible link between the 18-year-old arrested earlier today and the three Cardiff jihadists who recently appeared in a recruitment video for militant group Isis.
It says anti-terror police are currently investigating the connection.
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.
A man accused of posting a string of terrorist publications on Facebook was remanded in custody at the Old Bailey today.
Khuram Shazad Iqbal, 20, also allegedly had ten copies of an Al Qaeda magazine on his home computer when arrested on October 8th.
It is alleged Iqbal, of Kings Road, Cardiff provided a service for others to obtain, read, listen or look at terrorist publications on a Facebook page.
Iqbal appeared in court via videolink wearing a white head cap and light coloured top with a long black beard and spectacles.
He is accused of publishing material to incite terrorism and possessing a record containing information useful to terrorism.
He spoke only to confirm his name during the 15 minute hearing. Mr Justice Sweeney adjourned the case until February next year for a plea and case management hearing.
A Cardiff man who admitted helping others to prepare for acts of terrorism has had an appeal against his sentence dismissed.
Omar Latif was jailed for 10 years and four months, with another five years on extended licence.
He was jailed in February 2012, alongside brothers Addul Miah and Gurukanth Desai, also from Cardiff, who plotted to bomb the London Stock Exchange.
They did not appeal their terms.
They were part of a group of nine, with others from London and Stoke, which met in Cardiff.
A man from Penarth who survived the 7/7 bombings in London, but then faced deportation from the UK due to a technicality over citizenship, has now, finally, won his right to stay. Professor John Tulloch says he's 'delighted' to now be granted British citizenship.
He was born to British parents in India before independence. This only conferred a lesser British nationality, and, when he got an Australian passport in the 1990s, he inadvertently voided his right to live in Britain.
Now, after his story was covered and provoked a public outcry, he has been granted British citizenship. 'It has been an absolute nightmare. I've been trying for so many years to get my British passport back', he said. He now hopes to get a British passport formally by Christmas.
A man from the Vale of Glamorgan who survived the 7/7 terror attacks in London is facing the possiblity of being deported. John Tulloch from Penarth was brought up in the UK but born in India while it was a British Colony. David Wood has been speaking to him.
No further action is being taken against four men arrested in south and mid Wales in February on suspicion of being in possession of funds for terrorist purposes.
Officers from the Metropolitan Police's Counter Terrorism Command arrested a 34-year-old man and a 45-year-old man in Pontardawe, a 38-year-old man in Swansea and a 37-year-old in Ceredigion. All four have now been released from bail.
A man from Cardiff is due to appear in court after a series of co-ordinated raids by the Metropolitan Police's counter-terrorism command.
Daud Ali, 40, is one of three men who have been charged with conspiracy following raids at four properties in Cardiff, Coventry and London on Tuesday.
Officers were investigating a network suspected of funding terrorism. All three were held under the terrorism act and questioned by detectives before being jointly charged with conspiracy for allegedly mislabelling parcels which were being exported out of the UK.
Daud Ali from the St Mellons area of the city was also charged under the identity documents act for allegedly possessing a fake Norwegian passport.
The three men are due to appear before Westminster Magistrates' Court later today.