The Bush administration has just recently decided to designate a large chunk of a sovereign nation's armed forces as a terrorist organization. The choice doesn't seem to be final and hasn't been put into effect yet, so it might just be saber rattling to pressure the Iranian government, although it's hard to see what effect this would actually have on the Iranian regime, which is already the target of US economic sanctions.
What's interesting about this is that it's the first time the US has decided to label a state actor as a terrorist organization. The current definition contained in Title 18 of the US Code, Section 2331 is as follows:
Section 2331. DefinitionsAs used in this chapter -
(1) the term "international terrorism" means activities that -
(A) involve violent acts or acts dangerous to human life that
are a violation of the criminal laws of the United States or of
any State, or that would be a criminal violation if committed
within the jurisdiction of the United States or of any State;
(B) appear to be intended -
(i) to intimidate or coerce a civilian population;
(ii) to influence the policy of a government by
intimidation or coercion; or
(iii) to affect the conduct of a government by mass
destruction, assassination, or kidnapping; and
(C) occur primarily outside the territorial jurisdiction of
the United States, or transcend national boundaries in terms of
the means by which they are accomplished, the persons they
appear intended to intimidate or coerce, or the locale in which
their perpetrators operate or seek asylum;
What is interesting is that this definition, contrary to many others, does not exclude state actors. As such, every time the CIA or IDF kidnaps or assassinates someone, those organizations are committing acts of international terrorism, according to US Code. People like Noam Chomsky have held the US to its definition for a very long time, but until now, there has been a hesitancy about designating any state actors as terrorist organizations, presumably because that opens the US Government, and those of its allies, even more so to charges of terrorism.
If I were part of the Iranian government, I would bring this up and make a similar designation of the US Government. After all, at a time when CIA agents have been indicted by an Italian judge for kidnapping, it's a charge that is difficult to rebut.