WASHINGTON — Government investigators said Friday that they had discovered classified information on the private email account that Hillary Rodham Clinton used while secretary of state, stating unequivocally that those secrets never should have been stored outside of secure government computer systems.

Mrs. Clinton has said for months that she kept no classified information on the private server that she set up in her house so she would not have to carry both a personal phone and a work phone. Her campaign said Friday that any government secrets found on the server had been classified after the fact.

But the inspectors general of the State Department and the nation’s intelligence agencies said the information they found was classified when it was sent and remains so now. Information is considered classified if its disclosure would likely harm national security, and such information can be sent or stored only on computer networks with special safeguards.

“This classified information never should have been transmitted via an unclassified personal system,” Steve A. Linick, the State Department inspector general, said in a statement signed by him and I. Charles McCullough III, the inspector general for the intelligence community.