Mike McCurry, the White House spokesman, said that a statement issued by the agency on Thursday had left "a lot of questions unanswered"and that the White House was prepared to order the dismissal of CIA officers if an investigation showed that they had withheld information.
The widow of the murdered guerrilla, Jennifer Harbury, said that she would bring a lawsuit against the US government if the CIA continued to hide details about the fate of her husband, kidnapped in 1992.
Ms Harbury obtained confirmation on Thursday of her suspicion that her husband, Efrain Bamaca Velasquez, had been murdered when Congressman Robert Torricelli, a Democrat on the House Intelligence Committee, announced that Colonel Julio Roberto Alpirez, then allegedly on the the CIA payroll, had ordered Mr Bamaca's torture and execution.
In 1990, Mr Torricelli said, the colonel also had ordered the murder of Michael Devine, an American hotel entrepreneur.
The congressman, who has written a letter to President Clinton seeking more information, said he had learnt that Mr Bamaca's killing occurred in July 1992 - during George Bush's administration - and that between October 1992 and January 1993 White House and State Department officials had been told the facts of the case.