By Zachary Cohen, Jake Tapper, CNN

(CNN) — Secretary of Defense Pete Hegseth risked compromising sensitive military information, which could have endangered American troops and mission objectives, when he used Signal in March of this year to share highly-sensitive attack plans targeting Houthi rebels in Yemen, according to four sources familiar with the contents of a classified Inspector General report.

The repercussions of Hegseth’s action, two sources told CNN, are less clear since the IG concluded that the defense secretary has the authority to declassify information and Hegseth asserted he made an operational decision in the moment to share that information, though there is no documentation of such a decision.

An unclassified version of the report is set to be publicly released Thursday. The classified report was sent to Congress on Tuesday night.

Messages sent from Hegseth’s Signal account to the group chat, the contents of which sources previously confirmed to CNN included material from documents marked classified at the time they were sent, offered specific, real-time updates about planned military strikes. They were so specific that one even read: “This is DEFINITELY when the first bombs will drop.”

It remains unclear if Hegseth properly declassified that information before sharing it with other top Trump officials, and a reporter, the Atlantic’s Jeffrey Goldberg?, who was accidentally added to the chat.

Hegseth refused to sit for an interview with the inspector general and submitted his version of events in writing, sources told CNN.

The IG’s findings are memorialized in a broader report produced after its months-long investigation into Hegseth’s use of Signal.

The report states that Hegseth should not have used Signal and that senior Defense Department officials need better training on protocols, the sources said.

The Pentagon did not respond to a request for comment.

The release of the investigation could compound existing concerns voiced by lawmakers from both sides of the aisle about Hegseth’s judgement and bring renewed attention to an issue that nearly led to his firing several months ago, CNN has reported.

Hegseth and his inner circle have been bracing for months – but had hoped the release of the report would mark the final chapter of what has been a prolonged political headache for the Trump administration.

Beyond concluding that Hegseth’s actions could have endangered American troops, the report also details how he shared highly sensitive information with unauthorized individuals and failed to preserve those communications – as required under federal law, sources said.

In addition to the Signal chat that included several other senior Trump officials and, unbeknownst to Hegseth at the time, a reporter, the IG report found that the defense secretary shared similar details, via Signal, about US military operations in Yemen with several other people who were not authorized to review the information, the sources said.

Hegseth’s account shared details about the anti-Houthi military operation in at least two separate Signal group chats, one of which included his wife, brother, and personal lawyer, CNN has reported. One witness told the inspector general’s office over the course of the review that they recalled being a part of about a dozen separate Signal chats that included Hegseth, but it’s not clear if they all contained sensitive operational details, CNN also reported.

The watchdog also found that the military plans disclosed by Hegseth’s account were taken from a US Central Command document that was marked classified at the time, the sources said.

The document was marked Secret/NOFORN, meaning no foreign nationals should see it, CNN has reported.

Hegseth maintains his original classification authority, which allows him to unilaterally declassify information, undercuts any allegations of potential wrongdoing and that his use of Signal did not run afoul of preservation obligations for top officials under the Federal Records Act, according to a source familiar with his thinking.

The report, according to sources, also references a larger review of how Signal is used by federal officials and notes how the current regulations are set up in a way that they do not account for messages sent on the app or others like it. It specifically details how Hegseth used Signal from his office at the Pentagon – a secure space, meaning personal devices are prohibited inside – by having staff hardwire the app in a way that he could access it without needing physical access to his phone.

?The IG examined whether anyone else could have physically entered the information into the Signal chat – named PC Houthi Small Group – at Hegseth’s request, and asked witnesses whether others had access to his phone, CNN has reported.

The Air Force Office of Investigations separately is looking into whether other people, like Hegseth’s chief of staff, facilitated any unauthorized disclosures of classified info by using the secretary’s electronic devices.

This story has been updated with additional details and to include a complete quote.

CNN’s Natasha Bertrand contributed to this report

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