Factions of the Iranian government were behind an alleged plot to use explosives to assassinate the Saudi ambassador to the United States with help from a purported member of a Mexican drug cartel, U.S. officials say.

U.S. Attorney General Eric Holder said the criminal complaint, filed in New York, alleges that "this conspiracy was conceived, sponsored and directed from Iran."

"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."

Two people, including a member of Iran's special operations unit known as the Quds Force, were charged in New York federal court. The charges included conspiracy to murder a foreign official, conspiracy to use a weapon of mass destruction and conspiracy to commit an act of international terrorism transcending national boundaries.

Manssor Arbabsiar, a 56-year-old U.S. citizen who also holds an Iranian passport, was charged along with Gholam Shakuri, whom authorities said was a Quds Force member. Arbabsiar was arrested but Shakuri remains at large.

"We will not let other countries use our soil as their battleground," Preet Bharara, the U.S. attorney in Manhattan, said at a news conference in Washington with Holder and FBI Director Robert Mueller.

The criminal complaint alleges that Arbabsiar and his Iran-based co-conspirators, including Shakuri, had been plotting to kill Saudi diplomat Adel Al-Jubeir from the spring of 2011 to October.

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Attorney General Eric Holder says two suspects have been charged in New York for their alleged participation in a plot to murder the Saudi Ambassador to the U.S. ((Haraz N. Ghanbari/Associated Press))

Arbabsiar unknowingly arranged to hire a Drug Enforcement Administration source, who was posing as a member of a drug trafficking cartel,  to carry out the plot, the complaint alleges.

Arbabsiar wired approximately $100,000 to a bank account in the U.S as a down payment for the killing, the complaint alleges.

On May 24, 2011, Arbabsiar is alleged to have met with the DEA source. Arbabsiar allegedly asked the source about his knowledge of explosives and then explained he was interested in attacking a Saudi Arabia embassy, according to the complaint.

Arbabsiar allegedly met with the source several more times in Mexico, according to the complaint. In mid-July, the source allegedly told Arbabsiar he would need  four men to carry out the ambassador’s murder and that his price for carrying out the murder was $1.5 million. Arbabsiar allegedly agreed and stated that the murder of the ambassador should be handled first, before the execution of other attacks, the complaint states.

In another meeting in Mexico, the source allegedly told Arbabsiar that the attack could result in mass casualties of innocent bystanders, according to the complaint. But Arbabsiar allegedly said he didn't care and that the attack had to be carried out.

"Arbabsiar allegedly discussed bombing a restaurant in the United States that the ambassador frequented," according to the complaint. "When [the source] noted that others could be killed in the attack, including U.S. senators who dine at the restaurant, Arbabsiar allegedly dismissed these concerns as 'no big deal.'"

The complaint says that on Sept. 28, when Arbabsiar tried to fly to Mexico to guarantee final payment for the plot, he  was denied entry and placed on a return flight. A day later, Arbabsiar was arrested by federal agents during a flight layover at JFK International Airport in New York.

Arbabsiar allegedly confessed to his participation in the assassination plot.

"Arbabsiar also admitted to agents that, in connection with this plot, he was recruited, funded and directed by men he understood to be senior officials in Iran’s Quds Force," according to the complaint.

"He allegedly said these Iranian officials were aware of and approved of the use of [the DEA source] in connection with the plot; as well as payments to [the source]; the means by which the ambassador would be killed in the United States and the casualties that would likely result."

Asked whether the plot was blessed by the top echelons of the Iranian government, Holder said the Justice Department was not making that accusation.

Shakuri remains at large. Arbabsiar was arrested Sept. 29 at New York's John F. Kennedy International Airport. He was scheduled to appear in federal court Tuesday. Prosecutors said he faces up to life in prison if convicted.

U.S. President Barack Obama was first briefed on the plot in June, said White House spokesman Tommy Vietor.

"The disruption of this plot is a significant achievement by our intelligence and law enforcement agencies, and the president is enormously grateful for their exceptional work in this instance and countless others," Vietor said.

With files from The Associated Press