The State Department's inspector general is faulting U.S. diplomats in Japan -- including U.S. Ambassador to Japan Caroline Kennedy -- for conducting official business on private email accounts.

The report comes as former Secretary of State Hillary Clinton is under fire for using a private email account and server as her sole email during her four years as America's top diplomat.

Officials said the U.S. diplomats' private email practices were reported and confirmed during a routine inspection of State Department operations in Japan between January and March of this year.

"In the course of its inspection, OIG received reports concerning embassy staff use of private email accounts to conduct official business," the report released Tuesday by State IG Steve Linick said. "On the basis of these reports, OIG's Office of Evaluations and Special Projects conducted a review and confirmed that senior embassy staff, including the Ambassador, used personal email accounts to send and receive messages containing official business. In addition, OIG identified instances where emails labeled Sensitive but Unclassified were sent from, or received by, personal email accounts."

State employees in Japan may have brought the matter to the IG's attention because the furor over Clinton's use of personal email erupted in early March, while IG personnel were in Japan gathering information for their review.

The IG report, dated this month and made public in redacted form Tuesday on the IG's website, said routine use of personal email for official business poses security risks and is contrary to State Department policy.

"Department policy is that employees generally should not use private email accounts (for example, Gmail, AOL, Yahoo, and so forth) for official business. Employees are also expected to use approved, secure methods to transmit Sensitive but Unclassified information when available and practical," the report said.

Clinton and her defenders have claimed that her use of a private email account was consistent with practices of past secretaries of state and permitted under the law and agency regulations. Clinton's allies have also noted that a federal law mandating transfer of official messages from private accounts to government ones was not signed until 2014, nearly two years after she left office.

However, an agency rule promulgated in 2005 states that it is "the Department's general policy that normal day-to-day operations be conducted on an authorized information system."

The IG report cites that policy, as well as a cable sent to State Department officials worldwide in 2011 -- during Clinton's tenure -- telling them to avoid using private email accounts for official business. The cable was sent under Clinton's name, but that is a routine practice for cables sent from Washington and does not indicate that Clinton personally issued or reviewed the directive.

A State Department spokesperson described as "positive" the overall findings of the broad review of agency activity in Japan -- a study normally conducted for embassies every five years. Asked about the criticism of private email use, the spokesperson -- who commented on condition of anonymity -- said the Tokyo embassy generally insists that official work be done on official accounts.

"In accordance with Department policy, the Mission requires the use of official email accounts to conduct official business whenever possible," the spokesperson said. "The use of private e-mail is allowed for government purposes, as long as certain rules are followed. The Mission periodically reminds employees of the importance of following these rules, laid out in the 2013 National Archives and Records Administration (NARA) guidance. These rules include ensuring that certain types of protected information are not transmitted in non-official channels and that records sent or received on private email accounts are preserved as required."

At a regular briefing for journalists Tuesday, State Department spokesman John Kirby repeated those comments nearly verbatim.

The mission in Japan is implementing all the recommendations, including the recommendations with respect to email traffic, "as we speak," Kirby said. "They've taken the recommendations very seriously."

Kirby said use of private email by State Department employees for work purposes is disfavored, but not banned.

"It is not prohibited to use private email. It is discouraged, obviously," he said. "We recognize there are circumstances where there may be no other choice."

Kirby also said Kennedy had abided by State Department rules, routinely uses an official government account for work and did not discuss classified information on her personal account. "There is absolutely no indication that she violated department policy. Department policy says only use it infrequently. She did only use it infrequently," he said.

The IG report on Japan is similar to dozens of other reports the IG's office has issued in recent years counseling against use of personal, private or commercial email accounts for department business.

UPDATE (Tuesday, 3:32 P.M.): This post has been updated with Kirby's comments.