During Desert Storm the US did drop 11 "Daisy Cutter" bombs on the Iraqis. They're the largest non-nuclear bomb in the US arsenal and they leave a mushroom cloud like a nuke when they detonate. British SAS thought the US nuked Baghdad when they first used them.
http://www.washingtonpost.com/wp-srv/natio...esponse_14.html
http://www.globalsecurity.org/military/sys...ions/blu-82.htm