LONDON - British police on Monday arrested 12 men on suspicion of plotting an act of terrorism, swooping in major pre-dawn raids across the country. Five suspected men were arrested from Cardiff, four from Stoke-on-Trent and three from London. The suspects, aged between 17 and 28, were detained by unarmed officers at around 5am. Metropolitan Police assistant commissioner John Yates, national lead for counter-terrorism policing, said: 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. The operation is being led by Metropolitan Police Deputy Assistant Commissioner Stuart Osborne, the senior national co-ordinator of terrorist investigations, and involves police from forces in London, South Wales and Staffordshire. West Midlands Police said in a statement: All were arrested at or near their home addresses, with the exception of one suspect from Stoke who was at a domestic property in Birmingham. Searches are now being conducted at the home addresses, plus the address in Birmingham and another residence in London. The suspects will be held at police stations in central London, the North West and the West Midlands. The arrests come after intelligence agencies in Europe, Pakistan and the US intercepted a credible plot to launch raids on European cities, in a similar style to the attacks in Mumbai, India, two years ago. Sky News Channel reported that the arrests are not linked to the Mumbai-style plot but are allegedly part of a separate plot entirely the men are thought to have connections with Bangladesh. The UKs terror threat rating remains at severe, the second highest rating, meaning a terrorist attack is highly likely.