The United States said Tuesday it had broken up a "chilling" plot planned high up in the Iranian government to assassinate the Saudi envoy to Washington and vowed to hold Tehran to account.
In an explosive twist to the bitter US showdown with the Islamic Republic, the Justice Department charged two men with conspiring with Iranian government factions to blow up Saudi Ambassador Adel Al-Jubeir on American soil.
"The complaint alleges that this conspiracy was conceived, sponsored and directed from Iran and constitutes a flagrant violation of US and international law," said US Attorney General Eric Holder.
"In addition to holding these individual conspirators accountable for their alleged role in this plot, the United States is committed to holding Iran accountable for its actions," he said.
A criminal complaint named Manssor Arbabsiar, a 56-year-old naturalized US citizen holding Iranian and US passports, and Gholam Shakuri, an Iran-based member of Iran's Quds Force, a unit of the Iranian Islamic Revolutionary Guard Corps, in the plot.
Shakuri remains at large while Arbabsiar was arrested on September 29 at New York's John F. Kennedy airport and appeared in court Tuesday in Manhattan.
His lawyer said he would plead not guilty, if charged.
The alleged attack, dubbed by one top US official a "Hollywood" scenario, was broken open by a paid US source posing as a member of a "violent" Mexico-based drugs cartel known for "numerous" assassinations and murders.
The defendants believed the cartel would provide explosives for an attack on the ambassador, the complaint said.
One official said the assassination could have been followed by other "lethal" attacks plotted by Iran. Unconfirmed media reports said Israel's embassy in Washington could have been a target.
An aide to Iran's President Mahmoud Ahmadinejad dismissed the allegations as a "prefabricated scenario" designed to "turn public attention away from domestic problems within the United States."
But US Secretary of State Hillary Clinton said the United States would consult its allies about how to "further isolate" Iran.
News of the plot will sow even deeper distrust between fierce Gulf antagonists Iran and Saudi Arabia, amid the international standoff over Tehran's nuclear program.
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The Saudi embassy in Washington said the "attempted plot is a despicable violation of international norms, standards and conventions and is not in accord with the principles of humanity."
Holder said the plot against Jubeir, known as Saudi King Abdullah's closest advisor on foreign affairs, was directed and approved by elements of the Iranian government, and specifically, senior members of the Quds Force.
"High-up officials in those agencies ... an integral part of the Iranian government, were responsible for this plot," he said.
The Treasury Department froze US assets of Shakuri and Arbabsiar, and three others, Qasem Soleimani, Hamed Abdollahi and Abdul Reza Shahlai, who it said were senior Quds Force officers involved in the plot.
"Iran once again has used the Quds Force and the international financial system to pursue an act of international terrorism," said David Cohen, Treasury under secretary for Terrorism and Financial Intelligence.
Aides said that US President Barack Obama was first briefed on an alleged Iranian plot to kill the Saudi ambassador in June.
Robert Mueller, Director of the Federal Bureau of Investigation, said that the plot, which was disrupted before anyone was in imminent danger and explosives were bought, could have caused carnage.
"Though it reads like the pages of a Hollywood script, the impact would have been very real and many lives would have been lost," Mueller said.
The Justice Department said the plot was infiltrated partly by a US Drug Enforcement Agency agent posing as a member of the cartel.
Holder alleged that in a series of meetings, Arbabsiar set up an international conspiracy by the Iranian government to pay the supposed cartel $1.5 million to murder the ambassador.
Arbabsiar -- with Shakuri's approval -- then facilitated the wiring of approximately $100,000 into a US bank account as a down payment for the assassination attempt, the complaint said.
The Justice Department said Arbabsiar had confessed and provided testimony about the role in the plot of elements of the Iranian government.
Preet Bharara, US Attorney for the Southern District of New York, said the plot was "chilling" and alleged the confidential source named in the complaint had told one of the defendants an attack could take place in a restaurant holding up to 150 people. The defendant apparently answered "no big deal."