WASHINGTON — For the first time in more than a generation, a foreign power was accused Tuesday of plotting a political assassination in the United States capital, an allegation that stunned analysts who said it would seem to be an incredibly incautious move and a mark of desperation, if proved true.

Attorney General Eric Holder announced the charges against two Iranian-backed emissaries who the government alleged were arranging the killing of Saudi Arabia's ambassador to the United States, Adel al Jubeir.

At a news conference, Holder said the men were connected to the Quds Force, part of Iran's elite Revolutionary Guards. They allegedly met in May in Mexico to allegedly hatch the plot, which the attorney general said involved plans to pay $1.5 million for the hit.

Documents filed in a Manhattan federal court identified the suspects as Manssor Arbabsiar and Ali Gholam Shakuri, both originally from Iran and both alleged to have ties to the Quds Force.

Arbabsiar was described as a naturalized American citizen who was arrested on Sept. 29. The whereabouts of Shakuri, said to be a Quds Forces official, are unknown and he has eluded arrest.

"From the little we know, we caught a lucky break," said Matthew Levitt, an Iran expert for the Washington Institute for Near East Policy who was an anti-terror official during the George W. Bush administration. "Bottom line, this is tremendously significant if it ends up being true. This is an upping of the ante in the extreme, it's a sharp break in Iran's modus operandi."

McClatchy learned from multiple sources late Tuesday that the two indicted men also had discussed potential terror attacks against Saudi and perhaps Israeli diplomats in the Argentine capital of Buenos Aires. It is unclear how far along those discussions had progressed. Argentina was the target of Iranian-backed terror attacks in the early 1990's.

The U.S. complaint does not mention the Argentine plots.

Iran has been the target of increasing financial sanctions by the United States and Europe for its nuclear ambitions and continued deception of the International Atomic Energy Agency. It is also the main regional rival of U.S. ally Saudi Arabia, where the dominant religious group, Sunni Islam, is sharply opposed to Shiite Islam, the dominant religious sect in Iran.

The criminal complaint, however, offered no specific motive for the alleged plot.

"The bottom line is it is just tremendously risky," said Levitt, adding it reflected that Iran is pushing back hard against something.

The last high-profile political assassination in Washington was the car bombing by agents loyal to Chilean strongman Augusto Pinochet that killed that nation's former ambassador to the United States, Orlando Letelier, on Sept. 21, 1976.

Holder said the two alleged plotters had not yet acquired explosives but had arranged for nearly $100,000 to be wired to a New York bank account in the name of the hired hit man as a down payment. The proposed hit man was actually an informant working for U.S. law enforcement.

The charging documents say that Arbabsiar, a resident of the Texas port city of Corpus Christi, came to the attention of U.S. authorities after reaching out to the informant, who had begun working for the Drug Enforcement Administration after drug charged against him were dropped in the United States.