The alleged plot by Iran to assassinate Saudi Arabia's ambassador to the United States is a sharp reminder terrorism is not just the purview of groups such as al-Qaida.

True, the U.S. State Department's list of nations supporting terrorism abroad has dwindled in recent years. But the list still exists because the behavior still exists, and Iran -- as in the past -- holds a position of prominence.

The U.S. Justice Department this week announced it had foiled a murder-for-hire scheme in which two Iranians with connections to the al-Quds force of Iran's Revolutionary Guard attempted to hire a Mexican drug cartel killer to assassinate Saudi Ambassador Adel Al-Jubeir in Washington in return for $1.5 million.

The two men involved were Manssor Arbabsiar, a naturalized U.S. citizen, and Gholam Shakuri, a member of Iran's Islamic Revolutionary Guard Corps. What the two didn't realize was that the Mexican hit man was actually a paid informant of the U.S. Drug Enforcement Administration.

Meetings and discussions over the assassination, as well as follow-on attacks on the Saudi and Israeli embassies, took place over the summer and into early autumn.

Arbabsiar, arrested by U.S. authorities, has been indicted by a U.S. court. Shakuri was indicted in absentia since he is in Iran.

"This case illustrates that we live in a world where borders and boundaries are increasingly irrelevant -- a world where individuals from one country sought to conspire with a drug-trafficking cartel in another country to assassinate a foreign official on United States soil," FBI Director Robert Mueller said.

Saudi Arabia's Embassy said the alleged plot was "a despicable violation of international norms, standards and conventions," and Saudi Prince Turki al-Faisal warned "someone in Iran is going to have to pay the price."

How high in the Iranian government involvement in the alleged plot goes is still a matter of conjecture, but the U.S. government believes "even if at the highest levels there was not detailed operational knowledge, there has to be accountability with respect to anybody in the Iranian government engaging in this kind of activity," President Barak Obama said.

Al-Quds is an elite unit within Iran's Revolutionary Guard and strongly connected to the government's and the county's most conservative Islamic leaders.

It is known to have trained members of Hezbollah in Lebanon and Hamas, the Palestinian group that frequently attacks Israel.

Other groups that have received support from Iran and al-Quds include Iraqi Special Group Shiite terrorists and supporters of Iraq's anti-U.S. cleric Moqtada Sadr.

In the wake of the alleged plot, the United States has conferred with its European allies and Arab states and is said to be planning to take the case -- and the evidence collected -- to the United Nations to garner international support for more sanctions again Tehran. It has also proscribed dealings with an Iranian air carrier.

Iran has denied any connection with the alleged plot, and even the plot itself.

"The Americans acted unprofessionally in their childish play against Iran," said Ali Larijani, Iran's speaker of Parliament. "The Americans want to divert attention from their own domestic problems as well as the awakening of the Muslim world by initiating a stupid mischief."

No theory has been put forward as to why Tehran may have wanted to assassinate the Saudi ambassador. That, as well as additional details of the alleged plot, are yet to come.