Ukraine declares martial law after Russian attack

Ukraine's President Petro Poroshenko has declared martial law as tension with Russia escalates over its seizure of three Ukrainian navy ships off the coast of Crimea. Ukraine says Russia rammed one of its ships and fired shots in an "act of aggression", while Russia said the ships had illegally entered its waters. The declaration of martial law is subject to parliamentary approval in Ukraine. Our correspondent in Moscow is Dan Ashby..