Ukraine tension: Russian politics expert on latest moves

Ukraine is to impose a state of emergency throughout the country and has urged its citizens to leave Russia as the government in Kyiv steps up its response to what it calls intensified aggression from Moscow. Diplomatic avenues out of the crisis seem to be closing down as Russian forces numbering nearly two-hundred thousand troops remain entrenched at the border. King's College professor of russian politics Dr Sam Greene spoke to Corin Dann.