Tensions between Russia and the West rose still further on Thursday when Nato declared that a missile defence site in Romania had become operational.

A battery of American SM-3 interceptors, designed to shoot down incoming missiles, was activated at Deveselu military base. A similar facility is due to become operational in Poland in 2018.

Only a handful of interceptors will be deployed at the two bases, enough to protect Europe against attack from a country possessing a small arsenal of nuclear missiles. The missile shield would be of minimal use against Russia, which has about 300 inter-continental ballistic missiles on land and scores more deployed on submarines.

Nonetheless, Russia claims to sees the missile defence plan as direct threat to the deterrent power of its own nuclear arsenal. “From the very outset, we kept saying that in the opinion of our experts the deployment of an anti-missile defence poses a threat to Russia," said Dmitry Peskov, the Kremlin spokesman.

He described how President Vladimir Putin had "repeatedly asked who that system was working against and who it would be working against in the future”.