Iran Ayatollah: 'Death to America' refers to US policies from the Daily Beast
"Iranian Supreme Leader Ayatollah Ali Khamenei said Tuesday that exclamations of “Death to America” refer to dislike for American policies—not an actual wish for the destruction of the country. Khamenei reportedly discussed the slogan while meeting with students for the anniversary of the Iranian hostage crisis."
I actually view this statement as a really good sign on the diplomatic front. The Supreme Leader has been making noises in the last month or so suggesting that he opposed the nuclear deal. This suggests not only the exact opposite, but that he's actually trying to counter the hard right opposition to the agreement among Iran's clerical ruling class.