<p>As hundreds of armed men surrounded a Ukrainian military base in Crimea on Sunday, world leaders and Ukraine's new prime minister urged Russian President Vladimir Putin to pull back his military.<br /><br /></p>.<p>US Secretary of State John Kerry called Russia's military incursion into Ukraine “an incredible act of aggression”—comments that came a day after Russian forces took over the strategic Black Sea peninsula of Crimea from Ukraine without firing a shot.<br /><br />In Kiev, the Ukrainian capital, Prime Minister Arseniy Yatsenyuk said there was no reason for Russia to invade Ukraine, and warned that “we are on the brink of disaster”.<br /><br />But so far, his new government and other countries have been powerless to react to Russian military tactics. </p>
<p>As hundreds of armed men surrounded a Ukrainian military base in Crimea on Sunday, world leaders and Ukraine's new prime minister urged Russian President Vladimir Putin to pull back his military.<br /><br /></p>.<p>US Secretary of State John Kerry called Russia's military incursion into Ukraine “an incredible act of aggression”—comments that came a day after Russian forces took over the strategic Black Sea peninsula of Crimea from Ukraine without firing a shot.<br /><br />In Kiev, the Ukrainian capital, Prime Minister Arseniy Yatsenyuk said there was no reason for Russia to invade Ukraine, and warned that “we are on the brink of disaster”.<br /><br />But so far, his new government and other countries have been powerless to react to Russian military tactics. </p>