In President Putin's eyes, the West promised back in 1990 that Nato would expand "not an inch to the east", but did so anyway.

That was before the collapse of the Soviet Union, however, so the promise made to then Soviet President Mikhail Gorbachev only referred to East Germany in the context of a reunified Germany. Mr Gorbachev said later that "the topic of Nato expansion was never discussed" at the time.