The Federal Bureau of Investigation foiled a plot to assassinate the Saudi Ambassador. There is evidence that the backed by factions of the Iranian government.
...At a news conference, Attorney General Eric Holder said two Iranians have been charged with conspiracy to murder a foreign official and conspiracy to commit an act of international terrorism, among other charges.
One of the suspects, an Iranian with U.S. citizenship, was arrested in New York last month; the other, an Iranian, remains at large...
That Iranian at large is "Gholam Shakuri, an Iran-based member of Iran’s Quds Force, a paramilitary division of that country’s Revolutionary Guard Corps."
One thing, though, the complaint makes clear that the original plan was that the Iranians wanted the Mexican Drug Cartel to kidnap the Saudi Ambassador, but kill him if necessary. As the plot evolves, the DEA informant says that the easiest thing would be to kill the Saudi Ambassador at a restaurant that he visits at least twice a week.
It's at this point that he asks whether or not the Iranians would accept collateral damage? It's made clear that they would prefer just the Saudi Ambassador killed -- no others. But, if the only way to kill him was to blow up the restaurant and risk others being killed, so be it.