WASHINGTON — The State Department has discovered a dozen emails containing classified information that were sent to the personal email accounts of Colin L. Powell and close aides of Condoleezza Rice during their tenures as secretaries of state for President George W. Bush.

Two emails were sent to Mr. Powell’s personal account, and 10 to personal accounts of Ms. Rice’s senior aides. Those emails have now been classified as “confidential” or “secret” as part of a review process that has resulted in similar “upgrades” of information sent through the personal email server that Hillary Clinton used while she was secretary of state from 2009 to 2013. The State Department did not say who sent the emails to Mr. Powell or to Ms. Rice’s aides, or who received the messages.

It is against the law to have classified information outside a secure government account.

Of the nearly 30,000 emails from Mrs. Clinton’s server that have been released by the State Department under a court order, 18 emails sent to or from her have also been classified as secret, and 1,564 others have been classified at the lower level of “confidential.”

Last week, the State Department said that 22 emails had now been classified as “top secret” and would not be released, and would have part or all of their contents redacted, or blacked out. A review of 3,700 more emails by the department and intelligence agencies continues.