There is no question at this point that the world is dealing with an international security crisis in Ukraine. The UNSC is in session and debating whether to hold a public debate on the issue. The UK wants the meeting open and Russia wants it closed. NATO is also holding a meeting. The upper house of the Russian parliament has unanimously passed a resolution authorizing the government to use force in Ukraine. Foreign Ministry spokesmen are saying that this may not be acted on immediately. That appears to be a disconnect with the reports of troops already in the Crimea. Russia is taking the position that those troops are authorized under the terms of the existing treaty. Here is a graphic from BBC which gives a good view of those treaty rights.
It is unquestionable that Russia is making official and practical threats. The question is just how far are they prepared to go with them. The BBC article that the graphic came from provides a thoughtful and interesting analysis of the overall situation.