“A member of the US Army has been arrested in the UK as part of an investigation by Counter Terrorism Policing, working closely with US authorities, US Military and the FBI,” the police said in a statement.

The 41-year-old man was arrested near Gloucester on Tuesday, November 10, on suspicion of offences under Sections 1 and 3 of the National Security Act 2023.

Police said officers were conducting searches at two locations in Gloucestershire as part of the investigation. Russia is the country to which the allegations relate.

Deputy Assistant Commissioner Vicki Evans, Senior National Coordinator for Counter Terrorism Policing, said the arrest and investigation were the result of close cooperation between British and American authorities.

“The allegations are serious and our investigation is very much ongoing,” Evans said, adding that the operation demonstrated the strength of the UK-US law enforcement and national security partnership.

FBI Director Kash Patel described the arrest as an important development in an investigation involving allegations of espionage, which he said were of the utmost concern to the United States and its allies.

“While this investigation is continuing, I want to send a clear message – this FBI has no tolerance for anyone who breaks their oath to the United States and whose actions endanger our national security and that of our partners,” Patel said.

He added that the FBI had made 167 counterintelligence and espionage arrests over the previous 21 months, marking a 53 per cent increase.

Patel also thanked UK Counter Terrorism Policing, MI5, UK Defence Counter Intelligence and the US Army Counterintelligence Command for their cooperation in the investigation.

Brigadier General Sean Stinchon, commanding general of the US Army Counterintelligence Command, said the case highlighted the importance of international cooperation in tackling security threats.

“The alleged conduct of a senior soldier, entrusted with sensitive information, is a sobering reminder that insider threats are real and persistent,” Stinchon said.

He also urged anyone who had witnessed suspicious activity to report it to their local counterintelligence office.

The man has been detained under the National Security Act 2023 and remains in custody at a London police station.

The investigation is being led by officers from Counter Terrorism Policing London, with enquiries continuing.

Police also clarified that the investigation was not connected to any other ongoing Counter Terrorism Policing investigations.