The State Department has said it had fired two employees and punished a third for looking at White House hopeful Barack Obama's passport files without appropriate authorisation.
Obama's campaign called the breach of security an "outrageous" invasion of privacy and demanded a full probe.
"These unauthorized accesses were detected by the State Department and they were immediately acted upon," said undersecretary Pat Kennedy yesterday, adding that the incidents took place at separate times in January, February and March.
"However, we are taking immediate steps to be able to assure ourselves that it is nothing more than imprudent curiosity," Kennedy told reporters.
"In each of these cases, the unauthorized access was caught by a monitoring system. When the monitoring system is tripped we immediately seek an explanation for the record access, and that is the case in each of the individual cases."
Spokesman Sean McCormack said the department's initial take was that it was a matter of "imprudent curiosity," and that an investigation had been launched into what was done with the information accessed.
"That is our initial take on the matter," McCormack said. He declined to say whether the information had made its way out of the State Department but added: "We are not being dismissive of any other possibility."
{{/usCountry}}"That is our initial take on the matter," McCormack said. He declined to say whether the information had made its way out of the State Department but added: "We are not being dismissive of any other possibility."
{{/usCountry}}Kennedy said that "in two cases the employees were immediately terminated, the third was disciplined."
The Illinois senator's campaign spokesman issued a scathing statement, admonishing the administration of President George W Bush for showing "little regard" for citizens' rights.