Arbabsiar, a 56-year-old naturalized U.S. citizen, and Shakuri, allegedly a member of Iran's Quds Force -- the special operations unit of the Iranian Islamic Revolutionary Guard Corps (IRGC) -- are said to have plotted to murder the ambassador using explosives.
Arbabsiar was arrested on September 29 at JFK airport in New York. Shakuri is based in, and by all account remains, in Iran.
"Though it reads like the pages of a Hollywood script, the impact would have been real," said FBI Director Robert Mueller during a press conference at the Justice Department. "We send a clear message that any attempts on American soil will not be tolerated."
"It is only working side by side that we are able to stop plots like this before they can take hold," Mueller said.
Preet Bharara, the U.S. Attorney for the Southern District of New York, called the plot "well funded" and "chilling."
Holder said that DOJ would be working with the White House, Treasury and State Departments to hold Iran accountable for the plot.
Holder said it involved "high up officials" in the military. He said he did not make the charge that government officials were aware or signed off on the attack.