What will the U.S. do? That's the big question as the tense situation in Ukraine continues. The Russian military is still in Crimea, which is in the southern part of the country and no one is backing down.The tension in Ukraine was obvious Tuesday at an air base in Crimea. The troops threatened to shoot members of the Ukrainian military if they continued to march towards them. After warning shots were fired everyone calmed down.Around the same time Secretary of State John Kerry visited Kiev, where 67 protestors died last month. Kerry promised a billion dollar aid package that will help the struggling Ukrainian economy get back on its feet.The Secretary of State also emphasized that the U.S. wants to de-escalate the Ukraine crisis. He also called out Russian President Vladimir Putin."He really denied there were troops in Crimea? I've spoken as directly to President Putin today as I can. It is not appropriate to invade a country, and at the end of a barrel of a gun, dictate what we are trying to achieve. That is not 21st century, G8, major nation behavior," says Secretary of State John Kerry.President Putin held a rare news conference Tuesday. He suggested a larger invasion would be a last resort, but well within Russia's rights."Even if I take a decision to use armed force, it will be legitimate, fully corresponding to the norms of international law. In this case it would also correspond to our interest in protecting the people who are closely tied to us historically, culturally, economically," says Russian President Vladimir Putin.During a school visit in Washington President Obama spelled out exactly what he thought of President Putin's explanation."There is a strong belief Russia's action is violating international law. President Putin seems to have a different set of lawyers making a different set of interpretations, but I don't think that's fooling anybody."U.S. defense officials say Russia tested an intercontinental ballistic missile. However, defense officials say it was not unexpected and Russia did notify the U.S.