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Authorities foiled a plot that was directed by factions of the Iranian government to assassinate the Saudi ambassador to the United States, Attorney General Eric Holder said Tuesday at a press conference.

A criminal complaint was unsealed in federal court in New York Tuesday naming  Manssor Arbabsiar and Gholam Shakuri as the two alleged plotters, both with ties to Iran. Arbabsiar has been jailed in New York since September and Shakuri remains at large.

The complaint alleges that Iran helped conceive, sponsor and direct the plot. Holder called the alleged plot a "flagrant violation of U.S. and international law" and said the U.S. will hold Iran accountable.

The allegations in the 21-page complaint may further isolate Iran, which has a track record of supporting international terrorism.

A spokesman for the Iran mission to the U.N. categorically rejects the “baseless allegations” of the assassination plot, Reuters reported. Israel, meanwhile, referred inquiries to the FBI. And Saudi Arabia called the alleged plot a "despicable violation of international norms."

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Last spring, Arbabsiar met a number of times with a DEA source in Mexico posing as a member of a sophisticated international drug-trafficking cartel, the complaint alleges. It was during these meetings that Arbabsiar allegedly offered the agent  money to assassinate Adel al-Jubeir, the ambassador. Arbabsiar allegedly wired $100,000 into a U.S. bank account in August as a down payment for the hit.

Shakuri, a member of Iran’s Quds Force, a special operations unit of the Iranian Islamic Revolutionary Guard Corps, allegedly approved the money transfer.

The two planned to use an explosive device to assassinate the ambassador outside a restaurant in Washington that the ambassador frequented, according to the criminal complaint. When the source warned that other people will be inside the restaurant, Arbabsiar allegedly said, "They want that guy (the ambassador) done, if the hundred go with him, f--- 'em."

The alleged plot would have maimed others and damaged nearby structures in the surrounding area.

Arbabsiar allegedly confessed to his participation in the alleged plot. Shakuri is believed to be in Iran.

The complaint says Arbabsiar confessed that his cousin Abdul Reza Shahlai was a high-ranking member of the Quds Force who told him to hire someone in the narcotics business to target Al-Jubeir.

U.S. authorities described Shakuri as Shahlai's deputy who helped provide funding for the plot.

Shahlai was identified by the Treasury Department in 2008, during George W. Bush's administration, as a Quds deputy commander who planned the Jan. 20, 2007, attack in Karbala, Iraq, that killed five American soldiers and wounded three others.

Arbabsiar, Shakuri and Shahlai and two others -- Qasem Soleimani, a Quds commander who allegedly oversaw the plot, and Hamed Abdollahi, a senior Quds officer who helped coordinate -- were sanctioned Tuesday by the Treasury Department for their alleged involvement. The department described all except Arbabsiar as Quds officers.

Arbabsiar, a naturalized U.S. citizen who holds an Iranian passport, was arrested on Sept. 28 at New York's JFK Airport, after a flight from Mexico. He was read the Miranda rights, but allegedly waived his rights and spoke with law enforcement.

He allegedly admitted his connection with the plot and was recruited and funded by men he understood were senior officials in the Quds.

Arbabsiar appeared briefly at a federal magistrate court in New York Tuesday dressed in a checkered blue shirt. His lawyer said he'll plead not guilty at his next appearance on Oct. 25.

Secretary of State Hillary Rodham Clinton said Tuesday that the complaints are well-founded and the alleged plot "crosses a line."

She told The Associated Press that, "the idea that they would attempt to go to a Mexican drug cartel to solicit murder-for-hire to kill the Saudi ambassador, nobody could make that up, right?"

President Obama reached out to the ambassador to express solidarity and underscored the belief that the plot was a flagrant violation of U.S. and international law.

Before Tuesday's announcement, Interpol -- the international police organization -- issued an alert obtained exclusively by Fox News that warned of plans to assassinate an ambassador in the U.S.

Holder said the U.S. government would be taking unspecified action against the Iranian government as early as Tuesday afternoon. Asked whether the plot was blessed by the top echelons of the Iranian government, Holder said the Justice Department was not making that accusation.

The two are charged with conspiracy to kill a foreign official, conspiracy to use a weapon of mass destruction and conspiracy to commit an act of international terrorism and other charges.

"This is not a trip wire for military action in Iran," a senior defense official said.

The Associated Press contributed to this report.