Washington's threat of "economic D-Day" collides with a small group of governments that account for most of what remains of Iran's foreign trade.

Iran's rial slumps to record low ahead of sanctions announcement; Tehran charges measures prove US failed in war, says it issued warnings against cooperating with pressure campaign

By Yasmine Ghania and Kanishka SinghCAIRO/WASHINGTON, Aug 24 (Reuters) - The U.S. threatened Iran with what it called "the greatest financial offensive ever marshalled" as it…