WASHINGTON — The State Department’s inspector general on Wednesday sharply criticized Hillary Clinton’s exclusive use of a private email server while she was secretary of state, saying that she had not sought permission to use it and would not have received it if she had.

The report, delivered to members of Congress, undermined some of Mrs. Clinton’s previous statements defending her use of the server and handed her Republican critics, including the party’s presumptive nominee for president, Donald J. Trump, new fodder to attack her just as she closes in on the Democratic nomination.

The inspector general found that Mrs. Clinton “had an obligation to discuss using her personal email account to conduct official business” with department officials but that, contrary to her claims that the department “allowed” the arrangement, there was “no evidence” she had requested or received approval for it.