LONDON — British police arrested nine people Wednesday in the central England city of Birmingham as part of a “major counterterrorism operation,” police said.

Police released no immediate details, but British media, citing unnamed security sources, reported that the plot involved a potential “Iraq-style” kidnapping of a Muslim soldier in the British army. The BBC and other news outlets reported that the intended victim had served in Afghanistan. They reported that the plot involved abducting, videotaping and executing the soldier, who has been placed under protective custody.

David Shaw of the West Midlands police said at a briefing that eight men were arrested in eight houses in predawn raids, and a ninth person, whose gender was not specified, was arrested on a highway in the Birmingham area just before the briefing.

The arrests were the “culmination of many months of activities,” said Shaw, adding that they constituted a “very big operation” for the area’s police force.

“The threat of terrorism has been growing over the years,” Shaw said. He declined to provide details of the operation and said some of the reporting on it was “potentially damaging to the investigation.”

Britain was rocked by Islamic extremist attacks in July 2005, when 52 people and four bombers were killed in attacks on subway trains and a bus. One of the bombers left a videotaped suicide message in which he cited the British government’s support for the U.S.-led wars in Iraq and Afghanistan as a chief motivation. A virtually identical attack two weeks later failed when the alleged attackers’ bombs failed to detonate. Five men are currently on trial in that case.

Wednesday’s arrests were not related to a similar large-scale attack, according to anonymous sources cited by the BBC, the Press Association and other media outlets. Rather, they said, it allegedly involved a kidnapping that would represent a new departure for radical extremist activity in Britain.