Your first link is Ron Paul worrying out loud. There are no actual threats being made there.
Your second link cites Buzzfeed as a source, and the Buzzfeed article[1] claims some unnamed low-level officials would like to kill Snowden. Yet these anonymously-quoted people also admit that they wouldn't do it unless they had approval from higher up. Pretty close, but still not a threat.
Your last link is about a retired government official making a joke in very poor taste.
None of these are actual threats, let alone by US officials. They're either idle musings, or bad jokes, or "I want to, but I'm not going to." I certainly don't agree with the people making these despicable statements, but they're qualitatively different from, "If you don't stop leaking state secrets, you will die."
http://www.foxnews.com/politics/2013/06/11/ron-paul-us-gover...
http://www.businessinsider.com/us-spies-talk-about-killing-s...
http://www.theguardian.com/world/2013/oct/03/edward-snowden-...