The State Department on Saturday released another 551 of Hillary Clinton’s e-mails from her time as President Obama’s secretary of state, including about 15 percent that had been given updated security classifications after the fact.

More than 1,000 pages of documents sent from Clinton’s private e-mail account included 81 messages upgraded to “confidential,’’ which is the lowest level of classification, and three to “secret,’’ said a State Department official.

The e-mails, which included deliberations on topics including policy toward Syria, Libya, and the South China Sea, had not been tagged as classified at the time they were sent, according to the official, who asked not to be identified. None of the latest messages had been labeled “top secret,’’ a designation given to 22 e-mails withheld from release in January.

Saturday’s release pushes the tally of Clinton’s e-mail disclosures to more than 45,000. Clinton, a Democratic presidential candidate, relied on a private e-mail account and home-based server to conduct government business as the top US diplomat from 2009 to 2013. Republican critics have said the practice constituted a mishandling of classified information, and could return to that subject in a candidates’ debate in South Carolina on Saturday.

Clinton has repeatedly said she didn’t mishandle information and sent no information marked as classified at the time.