A member of the US army has been arrested in the UK on suspicion of assisting a foreign intelligence service, which is allegedly Russia.
The 41-year-old man, who has not been named, was detained near Gloucester on Tuesday, on suspicion of offences under the National Security Act 2023.
He is being held over allegations in relation to section 1 of the act - obtaining or disclosing protected information, and section 3 - assisting a foreign intelligence service.
The Metropolitan Police said counter terrorism officers have been working closely with the FBI and US military in the investigation.
Officers are carrying out searches at two locations in Gloucestershire, the Met said.
The force added that the country to which the allegations relate is Russia.
The suspect remains in custody at a police station in London and the investigation is being led by officers from Counter Terrorism Policing London, as enquiries continue.
Deputy Assistant Commissioner Vicki Evans, senior national coordinator for Counter Terrorism Policing, said: "This significant arrest and investigation is a result of close collaboration between UK and US authorities.
"The allegations are serious and our investigation is very much ongoing.
"This activity demonstrates the strength of our UK and US law enforcement and national security partnerships, and I commend the work of all the teams involved.
"We will work together to take robust action against those we suspect of any criminal activity that could undermine our national security."
FBI director Kash Patel said: "This important arrest involves allegations of espionage, which is of the utmost concern to the United States and our 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."
He added: "This matter shows that partnerships are essential to protect our countries and I want to express my thanks to UK Counter Terrorism Policing, MI5, UK Defence Counter Intelligence, and the U.S. Army Counterintelligence Command for their outstanding work."
(c) Sky News 2026: US army member arrested in UK over 'allegations of espionage' involving Russia
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