It is not likely that any nation would drop a nuclear bomb on another nation, especially when that nation has thermonuclear capability and the ability to deliver such bombs even after sustaining a first strike. Hence, not Iran, not N. Korea, not Pakistan, not India and not the European countries would drop a nuclear bomb on another country unless first attacked. However, there is real danger that an Iranian sourced nuclear bomb, if it existed, or a dirty bomb, would be exploded in Israel. The US is also at great risk that terrorists would explode a nuclear or dirty bomb. Such weapons can enter countris in containers or be driven across a border. The maker of the bomb probably could be identified but could claim that it was stolen. Barak is wrong, and I don't think he is stupid but rather being intentionally misleading.
from the article: Barak to Haaretz: Iran won't drop nuclear bomb on Israel