British police swooped down on three cities in predawn raids Monday and arrested a dozen men in connection with a suspected plot against U.K. targets — the most high-profile terrorism raids in Britain in more than a year and a half.
Assistant commissioner John Yates, Britain's senior counterterrorism police officer, said the suspects were detained in London, in the central English city of Stoke-on-Trent and in Cardiff, Wales.
"The operation is in its early stages so we are unable to go into detail at this time about the suspected offenses," Yates said in a statement. "However, I believe it was necessary at this time to take action in order to ensure public safety."
The suspects, ages 17 to 28, were arrested on suspicion of the commission, preparation or instigation of an act of terrorism. Police said 11 of the suspects were arrested at or close to their homes at around 5 a.m., while the remaining man was detained at a property in the central English city of Birmingham.
Their homes were being searched.
Police confirmed that the men were detained by unarmed officers — indicating that any attack was unlikely to have been imminent.
The raids stemmed from a large-scale intelligence operation involving several weeks of surveillance. The arrests are not believed linked to the recent suicide bombing in Sweden.
The arrests are the most high-profile anti-terror raids in Britain since April 2009, when 12 men were detained in raids across northern England. All were released without charge, but authorities insisted they had thwarted a major al-Qaida bomb plot in the northern city of Manchester.
Yates said Monday's arrests followed close coordination by officers from several different cities. "This is a large scale, pre-planned and intelligence-led operation involving several forces," he said.
A British security official, speaking on condition of anonymity because of the sensitive nature of his work, said the arrests did not relate to any planned holiday season attack. Iraqi officials had claimed last week that captured insurgents believed the Stockholm bombing was part of a series of planned al-Qaida attacks against the U.S. and Europe during the Christmas season. Those claims were rejected by both British and German officials, who insisted there are no specific threats to their countries over the festive period.
In October, the U.S. State Department advised American citizens living or traveling in Europe to be wary amid reports that terrorists were planning attacks on a European city.
Larry Miller reported for NPR from London for this story, which contains material from The Associated Press.