State Department officials released part of an email Monday, sent to Hillary Clinton in 2009, that an inspector general had previously deemed "top secret."
In the email, Clinton aide Huma Abedin alerted the former secretary of state that North Korea has launched two short-range missiles.
The State Department had apparently attempted to reach Clinton on a secure phone line to inform her of the strikes, but Clinton was at the movies.
Abedin told Clinton the State Department officials "said they could not tell me on an unsecure phone" details of the strike before describing some details of the incident that were redacted because they were classified.
"If u need more info, u can call ops from your secure phone and they can give u all," Abedin wrote. "They just couldn't disclose anything on an open line."
The July 3, 2009 email was a point of fierce contention between the State Department and the intelligence community inspector general last summer, when the latter flagged it as containing "top secret" intelligence over the former's objections.
State Department spokesman John Kirby said Monday the email had been "provisionally upgraded" to the "secret" level and would be released in part among the final batch of Clinton's emails.
The record in question was one of two supposedly "top secret" records that touched off an FBI investigation into Clinton's use of a private server.