Twelve men, including five from south Wales, have been arrested during an anti-terrorist operation.
The men – five from Cardiff, four from Stoke-on-Trent and three from London – were detained on suspicion of the commission, preparation or instigation of an act of terrorism in the UK.
The suspects, aged between 17 and 28, were detained by unarmed officers about 0500 GMT today.
Assistant Commissioner John Yates, national lead for counter terrorism policing, says: “This is a large scale, pre-planned and intelligence led operation involving several forces.
“The operation is in its early stages so we are unable to go into detail at this time about the suspected offences.
“However, I believe it was necessary at this time to take action in order to ensure public safety.”