Oct. 11, 2011  -- FBI and DEA agents have disrupted a plot to commit a "significant terrorist act in the United States" tied to Iran, federal officials told ABC News today.

The officials said the plot included the assassination of the Saudi Arabian ambassador to the United States, Adel Al-Jubeir, with a bomb and subsequent bomb attacks on the Saudi and Israeli embassies in Washington, D.C. Bombings of the Saudi and Israeli embassies in Buenos Aires, Argentina, were also discussed, according to the U.S. officials.

U.S. Attorney General Eric Holder said in an announcement today that the plan was "conceived, sponsored and was directed from Iran" by a faction of the government and called it a "flagrant" violation of U.S. and international law.

"The U.S. is committed to holding Iran accountable for its actions," Holder said.

READ: U.S. Complaint in Alleged Iran-Directed Terror Plot (PDF)

FBI Director Robert Mueller said the arrest of a suspect in the plot shows the U.S. will "bring the full weight of [the] law to bear on those responsible" and that "any attempts on American soil will not be tolerated."

Senior Obama administration officials said the U.S. currently does not have any information indicating that either Iranian Supreme Leader Ayatollah Ali Khamenei or President Mahmoud Ahmadinejad necessarily knew about the assassination plot and said the U.S. will pursue a path of response that would not include the possibility of an armed conflict with Iran.

READ: U.S. Will Not Respond Militarily to Iran Over Assassination Plot

Shortly after Holder publicly announced the foiled plot, the U.S. Treasury announced it was initiating sanctions against five people allegedly connected to the plot.

The stunning allegations come against a backdrop of longstanding tensions between Iran and the United States and Saudi Arabia. In the last year, Saudi Arabia has attempted to build an anti-Iran alliance to push back against perceived aggression by Iran in the region.

An Iranian representative in Washington, D.C., told ABC News the U.S. government's story was "fake" but declined to provide any other information.

In a pair of reports on different Iranian state-sponsored news outlets, Iranian officials rejected the charges, calling the plot a "prefabricated scenario" and the start of a "new propaganda campaign against Iran."

The State Department has listed Iran as a "state sponsor" of terror since 1984. Officials in Argentina have said Iran was behind an attack on the Israeli embassy in Buenos Aires in 1992.

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Alleged Terror Plotter Claims He Was 'Directed By High-Ranking' Iranian Officials

The new case, called Operation Red Coalition, began in May when an Iranian-American from Corpus Christi, Texas, approached a DEA informant seeking the help of a Mexican drug cartel to assassinate the Saudi ambassador, according to counter-terrorism officials.

The Iranian-American thought he was dealing with a member of the feared Zetas Mexican drug organization, according to agents.

The DEA office in Houston brought in FBI agents as the international terror implications of the case became apparent.

The Iranian-American, identified by federal officials as Manssor Arbabsiar, 56, reportedly claimed he was being "directed by high-ranking members of the Iranian government," including a cousin who was "a member of the Iranian army but did not wear a uniform," according to a person briefed on the details of the case.

Arbabsiar and a second man, Gohlam Shakuri, an Iranian official, were named in a five-count criminal complaint filed Tuesday afternoon in federal court in New York. They were charged with conspiracy to kill a foreign official and conspiracy to use a weapon of mass destruction, a bomb, among other counts. Shakuri is still at large in Iran, Holder said.

Holder identified Shakuri as an Iran-based member of the Quds force, a much feared special unit in Iran's Revolutionary Guard. The Treasury sanctions named several other members of the Iranian Quds force as well.

Arbabsiar, a naturalized U.S. citizen, expressed "utter disregard for collateral damage" in the planned bomb attacks in Washington, according to officials.

The complaint describes a conversation in which Arbabsiar was allegedly directing the informant to kill the Saudi ambassador and said the assassination could take place at a restaurant. When the informant feigned concern about Americans who also eat at the restaurant, Arbabsiar said he preferred if bystanders weren't killed but, "Sometimes, you know, you have no choice, is that right?"

U.S. officials said Arbabsiar met twice in July with the DEA informant in the northern Mexico city of Reynosa, across the border from McAllen, Texas, and negotiated a $1.5 million payment for the assassination of the Saudi ambassador. As a down payment, officials said Arbabsiar wired two payments of $49,960 on Aug. 1 and Aug. 9 to an FBI undercover bank account after he had returned to Iran.

Federal agents said the DEA and the FBI recorded a number of meetings and phone calls between the informant and Arbabsiar, some of them from Iran.

Officials said Arbabsiar flew from Iran through Frankfurt, Germany, to Mexico City Sept. 29 for a final planning session, but was refused entry to Mexico and later put on a plane to New York, where he was arrested.

Arbabsiar also reportedly told the undercover DEA informant that his contacts in the Iranian government could provide "tons of opium" for the Mexican cartels, according to officials who have reviewed the case file.

Officials said Arbabsiar is now cooperating with prosecutors and federal agents in New York, where the case has been transferred.

"Though it reads like the pages of a Hollywood script, the impact would've been very real and many lives would've been lost," Mueller said of the foiled plot.

The public defender representing Arbabsiar did not immediately return requests for comment on this report.

ABC News' Lee Ferran and Jake Tapper contributed to this report.

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