"I want to thank the intelligence and law enforcement communities for their dedicated and outstanding work in thwarting this attempted attack," Gillibrand said. "Iran has shown the world once again it poses an existential threat to the world community. We must stand together and make it crystal clear - we cannot, and will not, tolerate a nuclear Iran that would pose an even greater threat.

"That is why Congress must pass the Iran, North Korea, and Syria Sanctions Consolidation Act, my bi-partisan legislation that increases economic pressure on Iran. Until Iran halts its nuclear ambitions, we must do everything in our power to enforce sanctions and choke them off from the global economy."

Earlier on Tuesday, Holder announced that two suspects had been charged with plotting to kill the Saudi ambassador to the U.S. The Department of Justice said that elements of the Iranian government and Mexican drug cartels were involved in the foiled plot.

Washington D.C. Mayor Vincent Gray (D) praised the operation and said he had been "updated" on the plot since July.

"I am grateful to the FBI and other law enforcement agencies for disrupting the terror plot to assassinate the Saudi Arabian Ambassador and  to bomb the Saudi and Israeli embassies in the District of Columbia," Gray said in a statement. "I have been fully briefed and updated on this situation since July and am pleased to see the success of today’s operation to keep our city safe.  These threats are serious and citizens should know we are taking all appropriate measures to ensure their safety."

—This story was updated at 4:35 p.m.