A major national counter-terrorism operation has led to twelve men being arrested early on Monday morning.
Five from Cardiff, four from Stoke-on-Trent and three from London were picked up by police.
They're suspected of the commission, preparation or instigation of an act of terrorism in the UK.
The suspects are aged between 17 and 28 and were detained by unarmed officers at around 5am.
Police say searches are now taking place at their home addresses and two other properties in Birmingham and London.
The operation is being led by Metropolitan Police Deputy Assistant Commissioner Stuart Osborne, the Senior National Co-ordinator of Terrorist Investigations, and is being co-ordinated from the West Midlands Counter-Terrorism Unit.
It also involves the Metropolitan Police's Counter Terrorism Command, South Wales Police and Staffordshire police.
The arrests come after intelligence agencies in Europe, Pakistan and the US intercepted a credible Islamic plot to launch raids on European cities, in a similar style to the attacks in Mumbai, India, two years ago.
More than 170 people were killed during a 24-hour co-ordinated attack on Mumbai, also known as Bombay, by ten gunmen in November 2008. It has been blamed on Pakistani militants.
Home Secretary Theresa May was fully briefed on the raids before they took place.
