The newly released messages, which were posted on the State Department's Freedom of Information Act website, date from 2010 to 2011. The new production, which contains 3,849 additional new documents, accounts for 12 percent of the 52,000 pages in the State Department's possession, bringing the total amount of Clinton's email released to more than 37 percent.
Clinton has maintained she did not communicate classified information on her private account. But the documents released today show more email that has been deemed classified after the fact. The State Department said portions of 215 documents were upgraded to classified, bringing the total number of newly classified documents to over 400.
The reclassified and heavily redacted material included messages about conversations with Russian Foreign Minister Sergey Lavrov, Palestinian President Mahmoud Abbas, and Pakistani Prime Minister Yousuf Raza Gilani.
Another 2011 email showed then-Sen. John Kerry messaged Clinton on her private email account, meaning he knew she was using a non-government email address while at the State Department.
The batch released today included at least two pieces of email relating to long-time Clinton aide Huma Abedin's husband, Rep. Anthony Weiner, who resigned from Congress after posting lewd photos on social media. As the scandal brewed in June 2011, Cheryl Mills, Clinton's chief of staff at the State Department, forwarded Clinton articles about Weiner on at least two occasions.
Some of the email highlight frustrating, yet humorous moments for Clinton, including the time a White House operator who didn't believe who she was when she tried to call the White House.
One email showed Clinton's reaction when Rep. Gabby Giffords was shot in 2011. Her aide, Jake Sullivan, noted that initial reports said Giffords was "shot and killed." Clinton said, "I'm sick. I knew her and can't believe it."
In an interview with ABC News' David Muir earlier this month, Clinton apologized for the use of a private email account, acknowledging it was a "mistake.”
"As I look back at it now, even though it was allowed, I should have used two accounts: one for personal, one for work-related emails,” Clinton said. “That was a mistake. I’m sorry about that. I take responsibility.”
The State Department began releasing Clinton's work-related email from her private account in May and aims to release them in their entirety by January.
In response to the State Department's document release today, Reince Priebus, chairman of the Republican National Committee, criticized Clinton's use of a private email server.
“With the number of emails deemed classified doubling to more than four hundred, this latest court-ordered release shows Hillary Clinton put our national security in more jeopardy than previously known,” Preibus said. “Hillary Clinton said at the outset of her email scandal there was no classified material on her secret server, and this release is another reminder she has mislead the American people from day one. Hillary Clinton’s reckless attempt to skirt transparency laws and her dishonest response to public inquiries underscore why she can’t be trusted in the White House.”
ABC News' Justin Fishel contributed to this report.