(TNND) — The Pentagon's watchdog is investigating Defense Secretary Pete Hegseth's use of the messaging app Signal to discuss attack plans with other high-ranking national security officials.

The Signal group chat discussing U.S. military strikes on Houthi militants in Yemen came to light when journalist Jeffrey Goldberg of The Atlantic was inadvertently included in the app’s thread.

Hegseth has denied wrongdoing and shifted blame to Goldberg, who he called "deceitful and highly discredited."

"Nobody was texting war plans, and that’s all I have to say about that," Hegseth said after the story broke from The Atlantic.

Now, the Defense Department’s acting inspector general is looking into the situation.

The watchdog sent a letter Thursday to Hegseth, informing him that he was going to investigate whether the use of Signal, an encrypted but commercially available messaging app, complied with Defense Department policies.

Steven Stebbins, the acting inspector general, also said they’d examine compliance with classification and records retention requirements.

The inspector general investigation was requested by the Republican and Democratic leaders of the Senate Armed Services Committee.

“This chat was alleged to have included classified information pertaining to sensitive military actions in Yemen. If true, this reporting raises questions as to the use of unclassified networks to discuss sensitive and classified information, as well as the sharing of such information with those who do not have proper clearance and need to know,” Senate Armed Services Committee Chairman Roger Wicker, a Republican, and Ranking Member Jack Reed, a Democrat, wrote in a letter to the Pentagon’s inspector general.

Matthew Levinger, the director of the National Security Studies Program at George Washington University, said no commercial messaging app should be used by government officials to conduct official business.

“Full stop. That's why the government has its own computer networks and its computer systems,” Levinger said. “And so, clearly, this conversation should have been carried out over on the high side. In other words, on a top-secret network.”

Levinger said the transcripts of the Signal chat released by The Atlantic rose to the level of what he would deem to be classified information.

He said the chats included details about launch times and launch vehicles for the attacks on the Houthis last month.

“And particularly of concern were the times of the fighter jet takeoffs and projected strike times,” Levinger said. “And this means that this is some of the most sensitive information about attack plans that can be released ... that clearly needs to be kept utterly secret. Because if that information leaks, the Houthis could take countermeasures, including potentially attacking incoming warplanes, which would put U.S. Navy fighter pilots at risk.”

President Donald Trump was asked Thursday during a press gaggle aboard Air Force One about the Defense Department’s new investigation into the Signal app usage.

“You’re bringing that up again? Don’t bring that up again. ... That’s such a wasted story,” Trump said.

Levinger said Hegseth and the other Trump administration officials on the Signal chat were “extremely sloppy” with their handling of classified information.

Trump’s national security adviser Mike Waltz was also on the Signal group chat, along with Hegseth, Vice President JD Vance, Secretary of State Marco Rubio, Director of National Intelligence Tulsi Gabbard and others.

Levinger said the Trump administration has an obligation to ensure laws are followed for the protection of classified information and records retention.

“I see no evidence that the Trump administration had any interest in investigating this matter on its own accord and in making sure that the laws were followed,” he said.

Levinger’s colleague at GW, Peter Loge, the director of the School of Media and Public Affairs, said the bipartisan Senate request for an inspector general investigation shows some Republicans “are finding their feet a little bit and beginning to push back on the president.”

Loge noted that four other Senate Republicans joined Democrats to pass a resolution opposing Trump’s tariffs on Canada.

Loge said the Signal situation could be a one-off mistake by administration officials.

“But it becomes very easy for people to tell a story that this is one more example of an administration that really isn't up to the task of governing, fairly or not,” said Loge, referencing reports of Waltz’s use of Gmail for government business, the firings that had to be reversed for government officials who safeguard our nuclear materials, and other incidents that have come under scrutiny in the busy first months of the Trump administration.

Levinger said the Signal situation raises more questions about “what seems to be the administration's motto of ‘move fast and break things.’”

He said there are very clear rules for how sensitive information needs to be handled. It will be up to the Defense Department’s inspector general to determine if Hegseth and others followed those rules.