A flatbed rail wagon speeding through south-west Russia last week carried an ill omen for negotiations to avert a larger war with Ukraine.

On board was a Buk-M1, the kind of medium-range surface-to-air missile system that became notorious in 2014 after a missile fired from territory controlled by Russian proxies in eastern Ukraine shot down a Malaysian airliner, killing all 298 people aboard.

If Russia goes to war in Ukraine, it still needs to take a number of steps: establishing fuel supply lines, opening field hospitals and deploying air-defence systems such as the Buk that would protect its heavy weaponry and troops near the front.

Even as Joe Biden and Vladimir Putin were sitting down to talks meant to end the crisis, Russia was inching closer to being ready to launch a full-scale ground invasion of its neighbour.