The department said it gave Livia Acosta Noguera, Venezuela's consul general in Miami, until Tuesday to leave the United States after declaring her "persona non grata," the most serious form of censure a country can apply to a foreign diplomat, who is otherwise protected by diplomatic immunity from arrest and other normal kinds of prosecution.
Caracas was notified of the expulsion Friday, department spokesman Mark Toner said Sunday.
Acosta was allegedly involved in plans, with a group of Venezuelan, Iranian and Cuban diplomats, then based in Mexico, to attack the computer systems of the White House, FBI, CIA, Pentagon, National Security Agency and several nuclear power plants, the U.S.-based Spanish-language TV network Univision reported.
Iran's former ambassador to Mexico, Mohammad Hassan Ghadir, appeared in the documentary report last month and denied the accusations, which date from 2008.
The program and Miami's Spanish-language newspaper El Nuevo Herald tied Acosta to Venezuela's spy agency, the Bolivarian Intelligence Service.
Acosta's whereabouts where unclear Sunday. The Venezuelan consulate in Miami was closed, the Herald reported, and the Venezuelan Embassy in Washington said any statement about the expulsion would come from Caracas.
Caracas had no immediate comment. President Hugo Chavez did not mention it on his Sunday talk show, "Alo, Presidente," or "Hello, President," broadcast on Venezuelan state TV and radio for nearly 6 hours.
The expulsion announcement came the same day Iranian President Mahmoud Ahmadinejad, a close Chavez ally, arrived in Caracas to shore up support from the region's leftist leaders as tough new Western sanctions seek to isolate the Islamic republic and target its vital oil exports.
Chavez said Sunday he would meet with Ahmadinejad Monday. The two were then scheduled to be in Nicaragua Tuesday to attend the inauguration of President Daniel Ortega.
The Iranian leader was also to visit Cuba and Ecuador.
All the nations on Ahmadinejad's itinerary have governments opposed to U.S. influence in the region.
Representatives of the Venezuelan community in Miami urged the State Department to expand its probe into other Chavez consular staff in the United States.
"We ask that they deepen their investigation into consular officials who remain and represent a threat to U.S. security and its residents. They will continue the actions developed by Livia Acosta on U.S. soil," warned a statement from the Organization of Politically Persecuted Venezuelans in Exile.
Roger Noriega, a visiting fellow at the conservative American Enterprise Institute think tank and a former assistant secretary of state for the Western Hemisphere -- who broke the expulsion news before the State Department announced it -- said on Twitter Sunday night he believed the State Department had already ordered an investigation of Venezuela's U.S. diplomatic delegations because the department believed they were "full of Chavista spies."