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On Tuesday, gunmen shot and killed a Ukrainian officer at a military base outside the Crimean capital, Simferopol, and wounded two other servicemen. Ukraine blamed Russian troops storming the base, while Crimean police say that both the Ukrainian soldier and a member of the pro-Russia Crimean self-defense forces were killed by an unidentified sniper. An eyewitness tells the BBC that men armed with automatic weapons arrived at the base in two unmarked cars and attacked it, guns blazing.

The attack came after Russian President Vladimir Putin and Crimea's leader signed documents allowing Russia to annex the occupied province, and it marks a dangerous escalation in the showdown between Ukraine and its Western allies on one side and Russia on the other. Ukraine responded to the killing by authorizing its soldiers in Crimea to fire in self-defense. "The conflict is moving from a political one to a military one because of Russian soldiers," said Ukrainian Prime Minister Arseniy Yatsenyuk. "Today, Russian soldiers began shooting at Ukrainian servicemen and this is a war crime without any expiry under a statute of limitations."