State Department officials are set to release 2,900 pages of Hillary Clinton's private emails Thursday after falling short of a court order requiring them to publish those documents by New Year's Eve.

While the agency should have posted more than 8,000 pages of emails online at the end of last month, State officials blamed the holiday schedule for releasing just 5,500 pages on time. They vowed to catch up by publishing the remainder during the first week of January.

Citing the heavy burden imposed by screening so many documents for sensitive information in such a short period of time, the State Department also declined to include headers with subject lines or sender and recipient information in the initial batch, making the records difficult to read.

The agency's failure to post nearly 3,000 pages of emails online by the end of December marked its largest shortfall since it began releasing documents on a monthly basis in March.

The State Department also fell short of a court-ordered benchmark in July, but caught up in subsequent months.

Clinton faced renewed criticism for her handling of classified information last week after the State Department revealed the latest batch of emails contained 275 newly-classified messages.

Agency officials have maintained that all of the more than 1,200 emails that are now classified were upgraded retroactively, and that none were considered classified at the time they were written.

However, questions about whether a handful of the records should have been marked classified when they originated prompted an FBI investigation that shows no signs of winding down.

Investigators seized Clinton's private server in August and have reportedly begun recovering deleted emails from the hardware. Clinton erased one email she deemed personal for every work-related email she turned over to the State Department in December 2014.

But the personal nature of many of the emails included in the work-related batch, which is roughly 55,000 pages long, raises questions about the process by which Clinton's staff culled records for release.

For example, Clinton has defended her frequent exchanges with Sidney Blumenthal, a divisive former aide who was banned from working at the State Department, as nothing more than correspondence with an "old friend." She denied that Blumenthal worked for her in any kind of professional capacity.

However, hundreds of emails to and from Blumenthal were included in the work-related emails Clinton handed over to the government, suggesting their relationship was more than friendly.

A significant portion of the emails Clinton considered official records discuss issues unrelated to her work as secretary of state, such as notes about the outfits she wore in press interviews and exchanges with lobbyists and political strategists outside the State Department.

Thursday's batch of Clinton emails is expected to contain additional messages that have been upgraded to classified.

If counted as separate from the release of emails last week, the publication of 2,900 pages of records Thursday will mark the ninth time the State Department has posted a trove of Clinton's emails online.

The final Clinton email release is slated for Jan. 29.