Dozens of Hillary Clinton's emails from her tenure as secretary of state have been flagged by officials as containing classified data, according to a published report.

Officials told The Washington Times that 60 emails had been flagged through the end of July by investigators reviewing Clinton's correspondence. The officials told the paper the figure is likely to grow as they work their way through approximately 30,000 work-related emails that passed through Clinton's so-called "homebrew" server. The review process is unlikely to be completed until January of next year, shortly before the Iowa caucuses and the New Hampshire presidential primary, Clinton's first big tests as the Democratic presidential frontrunner.

A source familiar with the review confirmed to Fox News late Sunday that more classified emails had been identified, but had no comment on whether as many as 60 had been flagged. Intelligence Community Inspector General Charles McCullough III had previously said that 10 percent of emails from a sample review of 40 messages contained sensitive or classified information. McCullough also has informed members of Congress that Clinton's emails likely contained hundreds of disclosures of classified information.

According to the Times, nearly all contained classified secrets at the lowest level of "confidential" and one contained information at the intermediate level of "secret." The number reported by the paper does not include two emails identified by McCullough last week as containing "top secret" information. The Associated Press reported Friday that at least one of the messages discussed the CIA drone program in Pakistan.

The Times reports that the flagged emails have been reviewed and cleared for release under the Freedom of Information Act as part of an open-records lawsuit. Some of the emails have multiple redactions out of respect for classified information.

Meanwhile, the paper also reports that some State Department employees have alerted McCullough to irregularities in how messages from Clinton's server were handled by the department and by her attorneys. Among the concerns are a possible conflict of interest due to at least one State Department attorney's ties to Williams & Connolly, the law firm of Clinton's attorney, David Kendall.

Another concern involved storage of a thumb drive containing a digital archive of Clinton's inbox. According to the Times, when State Department employees first identified classified information in Clinton's e-mail in May, they dispatched a safe to Kendall's office, where he kept the drive for several additional weeks before turning it over to the FBI after McCullough flagged the two top secret emails.

Clinton has repeatedly denied any wrongdoing, though her denials have shifted from saying in March that that there was no classified e-mail on the server to denying having sent or received e-mail marked classified on her server, which was kept at her Chappaqua, N.Y. home. 

At an appearance in Iowa Friday, Clinton appeared to make a joke of the e-mail controversy when she raved about the popular social media app Snapchat.

"I love it," she said. "Those messages disappear all by themselves."

Fox News' Catherine Herridge contributed to this report.