WASHINGTON — The United States on Tuesday accused Iranian officials of plotting to murder Saudi Arabia’s ambassador to the United States in a bizarre scheme involving an Iranian-American used-car salesman who believed he was hiring assassins from a Mexican drug cartel for $1.5 million.

The alleged plot also included plans to pay the cartel, Los Zetas, to bomb the Israeli Embassy in Washington and the Saudi and Israeli Embassies in Argentina, according to a law enforcement official.

The plotters also discussed a side deal between the Quds Force, part of Iran’s Islamic Revolutionary Guards Corps, and Los Zetas to funnel tons of opium from the Middle East to Mexico, the official said. The plans never progressed, though, because the two suspects — the Iranian-American and an Iranian Quds Force officer — unwittingly were dealing with an informant for the Drug Enforcement Administration, officials said.

Attorney General Eric H. Holder Jr., who announced the murder plot at a news conference in Washington, said it was “directed and approved by elements of the Iranian government and, specifically, senior members of the Quds Force.” He added that “high-up officials in those agencies, which is an integral part of the Iranian government, were responsible for this plot.”