Analysis: When would Russia be most likely to invade Ukraine?

If a Russian cross-border offensive into Ukraine is to take place, experts say there are time constraints President Vladimir Putin will have to consider.

Professor Michael Clarke, the former Director-General of the Royal United Services Institute, says Russia will have to either "go military or go home" at some stage within the next three to four weeks.

Troop rotation, favourable ground conditions and the Beijing Olympics beginning on 4 February could all play a part in Moscow's plans, he added.

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