U.S. Justice Department charges that elements of Iran's government were behind a foiled plot on the life of Saudi Arabia's U.S. ambassador have boggled the minds of many Americans knowledgeable about both Iran and terrorism.

The alleged target and modus operandi – employing a Mexican drug cartel to blow up Ambassador Adel al-Jubeir at a Washington restaurant – are unusual, to say the least, for a government that has focused on political dissidents and theatres of war closer to home.

"Fishy, fishy, fishy,'' Bruce Riedel, a CIA veteran who was formerly in charge of the Near East and South Asia on the White House National Security Council, told IPS. "That Iran engages in assassinations is old news. That it would use a Mexican drug cartel would be new."

Iran has not been behind a political assassination in the United States since a year after the 1979 revolution, when an African-American convert to Islam, Daoud Salahuddin, killed the former press attaché at the Iranian Embassy, Ali Akbar Tabatabai, in a Washington suburb.

Iran was also responsible for assassinations of Iranian dissidents in Europe in the 1980s and early 1990s but used its own agents or members of Hezbollah, a Lebanese Shiite organization that Iran helped create following the 1982 Israeli invasion of Lebanon.

Hezbollah is believed responsible for the 1983 bombing of a U.S. Marine barracks in Beirut and a spate of other bombings and abductions in Lebanon.

More recently, Iran has allegedly backed local proxies responsible for the deaths of U.S. soldiers in Iraq and Afghanistan.

U.S. experts on Iranian spy agencies and tradecraft say the hare-brained scheme described in the Justice Department complaint does not resemble the operations of the Quds Force, the external arm of the Iranian Revolutionary Guards (IRGC). Al-Quds means Jerusalem in Arabic.

"Nothing about this adds up," said Kenneth Katzman, author of a book on the IRGC and expert on Iran at the Congressional Research Service.

"Iran does not use non-Muslim groups or people who are not trusted members or associates of the Quds force," Katzman said. "Iran does not blow up buildings in Washington that invites retaliation against the Iranian homeland."

Indeed, the timing would be extremely awkward for Iran, which is already facing growing isolation because of its nuclear program and domestic abuses of human rights.

This weekend, Ahmed Shaheed, the new U.N. special rapporteur on human rights to Iran, will release his first report, which is expected to excoriate the Iranian government for its treatment of its own citizens, especially in the aftermath of disputed 2009 presidential elections.

Early next month, the International Atomic Energy Agency is scheduled to share with its board members new information about alleged Iranian research into making a nuclear warhead. A new finding against Iran by the board of the nuclear watchdog group would increase pressure on Russia, China and members of the Nonaligned Movement to approve more sanctions against the Islamic Republic.

Iran has vehemently denied the U.S. allegations that Quds Force officers recruited an Iranian-American from Texas, Manssor Arbabsiar, as part of a plot to kill al-Jubeir by employing members of a Mexican drug cartel.

Katzman speculated that Arbabsiar, a former used car salesman who was apparently in financial difficulties, may have come up with the idea on his own. According to the official complaint, he contacted a member of the Los Zetas cartel who turned out to be an informant of the U.S. Drug Enforcement Agency (DEA), as well as a cousin in Iran who has connections to the Quds Force.

Mr. Arbabsiar was said to have wired nearly 100,000 dollars to the informant's bank account from Iran in September and to have promised 1.5 million dollars to do the deed. He was arrested earlier this month when he was refused entry to Mexico and put on a plane to New York.

It is possible that the Iranian cousin "agreed to support him in some way but was doubtful he could pull it off", Katzman said. "This was not a thoroughly vetted and approved terrorist plot."

Several U.S. intelligence experts expressed scepticism about the expertise of the DEA in evaluating such a sensitive case.

Riedel noted that the complaint refers to "elements" of the Iranian government, "which suggests that the administration doesn't think that all elements of the Iranian government were involved".

An Iranian source, speaking with IPS on condition he not be named, said that the Quds force would investigate the Iranian alleged to have participated in the plot "to find out if there is any personal interest" involved, suggesting an element of freelancing.

"It seems the Americans and Saudis need this propaganda to promote their policy against Iran at this time, given that they have occupied three Muslim countries in the world – Iraq, Afghanistan and Bahrain," the source added.

While Iranian-Saudi tensions are clearly on the rise, Riedel questioned why Iran would want to target the Saudi ambassador. Al-Jubeir, while close to Saudi King Abdullah, is not a member of the royal family and has functioned mostly as the King's translator and "favoured messenger boy", Riedel said.

Both Katzman and Riedel said they were troubled by the way in which the Obama administration has jumped on the case, with a news conference by the attorney general and high-profile statements by the president and secretary of state.

Given the current tensions in the region, "I hope they know where they want to take it," Riedel said.

Vali Nasr, a professor of international politics at the Fletcher School of Law and Diplomacy at Tufts University, told CNN that the United States should "make public all the details of this plot" to avoid feeding Middle Eastern conspiracy theories.

"It is only with clarity of facts that the United States can make a convincing case for why Iran's anti- American posture and violent tactics is not heroic bravado deserving of accolade, but a cynical gamble that endangers the whole region," Nasr wrote.