Caroline Kennedy, the United States ambassador to Japan, and several other senior American diplomats there have used personal email accounts to conduct State Department business, the inspector general for the department said in a report released Tuesday. The inspector general, Steve A. Linick, identified instances in which “sensitive but unclassified” information was sent and received on personal email accounts, the report said. The criticism of Ms. Kennedy and the other diplomats came as Hillary Rodham Clinton, who is seeking the Democratic nomination for president, has faced questions about her exclusive use of a personal email account when she was secretary of state. That account was run through a private server that Mrs. Clinton kept at her New York home. The report on the embassy in Japan said the inspector general’s office “has previously reported on the risks associated with using commercial email for official government business.” It added that “such risks include data loss, hacking, phishing and spoofing of email accounts, as well as inadequate protections for personally identifiable information.” The State Department’s policy, the report said, “is that employees generally should not use private email accounts (for example, Gmail, AOL, Yahoo and so forth) for official business.” It added that “employees are also expected to use approved, secure methods to transmit sensitive but unclassified information when available and practical.” On her personal account, Mrs. Clinton had messages with “sensitive but unclassified” information, according to the inspector general for the intelligence agencies. She also received emails with information that the inspector general said should have been marked as “top secret.” The F.B.I. is investigating how classified information was handled in connection with her account. Mrs. Clinton and her campaign aides have defended her use of the personal account, saying that it was permitted at the time under State Department rules and that there were no classified markings on the materials. The Japan report was also critical of other aspects of the embassy and of its management by Ms. Kennedy, who was appointed to her post in 2013. It said that the State Department had not addressed some security vulnerabilities at the embassy and that communication between senior embassy leaders and the rank and file needed to be improved. “Embassy staff members lack the guidance they need to make day-to-day decisions on optimal allocation of limited U.S. government resources,” the report said. The State Department’s spokesman, John Kirby, defended Ms. Kennedy during a news briefing on Tuesday in Washington. He said there was no indication that her email practices had violated department policy, which, he added, discourages the use of personal email accounts but says they can be used infrequently. “She did only use it infrequently,” he said. Mr. Kirby said the department was carrying out all the recommendations in the report.