An American soldier accused of spying for Russia was assigned to a key NATO force responsible for defending the continent, it has emerged. Military chiefs admitted the 41-year-old suspect had been “entrusted with sensitive information” in his role.

The senior soldier is accused of helping a Russian intelligence service and obtaining or disclosing protected information. A senior NATO military official said: โ€œWe can confirm that the American service member arrested by British police was assigned to NATOโ€™s Allied Rapid Reaction Corps (ARRC)โ€. FBI director Kash Patel admitted the case involves “allegations of espionage”.

The suspect was based at Imjin Barracks, near Innsworth in Gloucestershire. NATOโ€™s ARRC is based there and is responsible for propelling troops to the front line, and would co-ordinate the allianceโ€™s warfighting effort in the event of an invasion.

In 2006, ARRC took command of NATOโ€™s ISAF mission in Afghanistan as the Alliance expanded its operations into the south. NATO says the British-led force โ€œcan deploy across Europe to reinforce Allied defences, deter aggression and, if necessary, help recover territory taken by an enemyโ€.

It is considered โ€œan important part of NATOโ€™s collective defenceโ€. But the Kremlin denied it is behind the espionage conspiracy. Dmitry Peskov, Vladimir Putinโ€™s spokesman, said: “This arrest does not concern us in any way, and we do not know what it is connected to.

“We have nothing to do with it, and it has nothing to do with us.” Sir Ken McCallum, the head of MI5, warned in his annual threat update that Russia remains “aggressor number one”, with the West facing a โ€œlong-haul contestโ€.

And intelligence chiefs fear they will continue attempting to wreak havoc for years. He said: โ€œWe are planning on the basis that these risks will endure.

“Some of these vulnerabilities are inherent in handling an open society in a connected era, AI isnโ€™t going away, there isnโ€™t a probability that that will be something that is going to go away by the end of next year.

โ€œIrrespective of what happens in Ukraine, it is quite hard to see the Kremlin suddenly decide to rub along with us all after all. So we are planning that this is going to be a long-haul contest.”