Why are there tensions?

American officials have warned of the “very distinct possibility” of a Russian invasion of Ukraine in the next few days, after Russia forward-deployed hundreds of tanks, self-propelled artillery and even short-range ballistic missiles from as far away as Siberia to within striking range.

Moscow’s rhetoric has also grown more belligerent. Vladimir Putin has demanded legal guarantees that Ukraine will never join Nato or host its missile strike systems, concessions he is unlikely to receive. A flurry of diplomatic activity has done little to ease tensions.

Putin is also short on time. His troops cannot remain out of garrison indefinitely. By late winter he will probably have to launch an attack or draw down his forces, in what would look like a retreat. In the meantime the UK, US and others have to told their citizens to leave.