LONDON — A senior U.S. Army soldier was arrested in the U.K. on suspicion of assisting Russian intelligence, British police said Tuesday.

The 41-year-old man was arrested “as part of an investigation by Counter Terrorism Policing” near the ⁠city of Gloucester, ​in the west ⁠of England, London’s Metropolitan Police said in a statement, adding that he remained in custody at a police station in the British capital.

He was ​arrested ⁠on suspicion of ‌offences under sections 1 and 3 of the National Security Act, ‌the statement said. These relate to obtaining ‌or disclosing protected information and assisting a foreign intelligence service.

“The country to which the allegations relate is Russia,” the statement added.

FBI Director Kash Patel was quoted in the statement as saying that the arrest was “important” and “involves allegations of espionage, which is of the utmost concern to the United States and our allies.”

The FBI, he added, “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.”

Brig. Gen. Sean Stinchon, the commanding general of U.S. Army Counterintelligence Command, was also quoted in the police statement.

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

“This case demonstrates the strength of our partnerships and the resolve of the counterintelligence community,” he added. “I am grateful to the U.K. and the FBI for their professionalism and teamwork throughout this investigation.”

Calling the allegations “very serious,” Deputy Assistant Commissioner Vicki Evans, Britain’s senior national coordinator for counter terrorism policing, said the “investigation is very much ongoing.”

The investigation is not linked to any other ongoing counter terror operations, the statement said.

But the arrest comes at a time of heightened tensions around the threat from hostile states, with British security services saying Russia and Iran have both used proxies to commit crimes on U.K. soil.

Officials in the U.K. have said proxies linked to Iran have been behind a string of arsons and other attacks in Britain and other countries, many of them targeting the Jewish community and intended to sow fear.

The United States has moved military aircraft from an airbase in the United Kingdom amid threats from Iran.

A U.S. official confirmed to NBC News that several military aircraft had left RAF Mildenhall as the security posture there had increased.

At least eight air refueling tankers and three Ospreys left the base in Suffolk, eastern England, on Monday, flight tracking data showed.