White House press secretary Karoline Leavitt has said no classified information was posted to the Signal chat.

Republican Senator Roger Wicker, chairman of the Senate Armed Services Committee, said he and Rhode Island Senator Jack Reed, the committee’s top Democrat, plan to send a letter to the Trump administration requesting an inspector general investigation into the use of Signal.

They seek a classified briefing with a top administration official “who can speak to the facts” of the episode.

Top military official was not included in the chat

The chat was also notable for who it excluded: the only military attendee of the principals committee, the chairman of the Joint Chiefs of Staff.

Admiral Christopher Grady is currently serving in that position in an acting capacity because Trump fired former chairman General CQ Brown Jr in February.

National security adviser Mike Waltz was authorised to decide whether to include the Joint Chiefs chairman in the principals committee discussion, “based on the policy relevance of attendees to the issues being considered, the need for secrecy on sensitive matters, staffing needs, and other considerations”, the White House said in a January 20 memo.

The Pentagon said it would not comment on the issue, and it was not immediately clear why Grady, currently serving as the president’s top military adviser, would not be included in a discussion on military strikes.

Hegseth has refused to say whether he posted classified information onto Signal.

He is travelling in the Indo-Pacific and to date has only scoffed at questions, saying he did not reveal “war plans”.

Director of National Intelligence Tulsi Gabbard and CIA Director John Ratcliffe told members of the Senate Intelligence Committee on Tuesday that it was up to Hegseth to determine whether the information he was posting was classified or not.

Very specific texts were revealed

What was revealed was jaw-dropping in its specificity and includes the type of information that is kept to a very close hold to protect the operational security of a military strike.

But Hegseth’s spokesman, Sean Parnell, said in a statement Wednesday that “there were no classified materials or war plans shared.

“The Secretary was merely updating the group on a plan that was underway,” he said.

The Pentagon and White House have tried to deflect criticism by attacking Goldberg and The Atlantic. The magazine and Goldberg, however, repeatedly reached out to the White House before and after publication to gain additional context on the Signal chat and ensure that publishing the full texts would not cause harm.

In a response, Goldberg reported on Wednesday, Leavitt described some of the information as sensitive and said the White House would prefer it not be published.

In the group chat, Hegseth posted multiple details about the impending strike, using military language and laying out when a “strike window” starts, where a “target terrorist” was located, the time elements around the attack and when various weapons and aircraft would be used in the strike.

He mentioned that the US was “currently clean” on operational security.”

“Godspeed to our Warriors,” he wrote.

“1215et: F-18s LAUNCH (1st strike package)”

“1345: ‘Trigger Based’ F-18 1st Strike Window Starts (Target Terrorist is @ his Known Location so SHOULD BE ON TIME – also, Strike Drones Launch (MQ-9s)”

“1410: More F-18s LAUNCH (2nd strike package)”

“1415: Strike Drones on Target (THIS IS WHEN THE FIRST BOMBS WILL DEFINITELY DROP, pending earlier ‘Trigger Based’ targets)”

“1536 F-18 2nd Strike Starts – also, first sea-based Tomahawks launched.”

“MORE TO FOLLOW (per timeline)”

“We are currently clean on OPSEC” — that is, operational security.

A strike package includes the personnel and weapons used in an attack, including Navy F-18 fighter aircraft. MQ-9s are armed drones. Tomahawks are ship-launched cruise missiles.

Goldberg has said he asked the White House if it opposed publication and that the White House responded that it would prefer he did not publish.

Signal is encrypted but can be vulnerable

Signal is a publicly available app that provides encrypted communications, but it can be hacked. It is not approved for carrying classified information.

On March 14, one day before the strikes, the Defence Department cautioned personnel about the vulnerability of Signal, specifically that Russia was attempting to hack the app, according to a US official who was not authorised to discuss the matter publicly and spoke on the condition of anonymity.

One known vulnerability is that a malicious actor, with access to a person’s phone, can link his or her device to the user’s Signal and essentially monitor messages remotely in real time.

Leavitt is one of three Trump administration officials who face a lawsuit from The Associated Press on First and Fifth Amendment grounds.

The AP says the three are punishing the news agency for editorial decisions they oppose. The White House says the AP is not following an executive order to refer to the Gulf of Mexico as the Gulf of America.