An American reporter was accidentally included in a group chat in which senior officials in Donald Trump's government discussed conducting airstrikes on Yemen's Iran-backed Houthis earlier this month.
Jeffrey Goldberg, the editor-in-chief of The Atlantic magazine, was added to a group which included US vice president JD Vance, defence secretary Pete Hegseth, national security adviser Mike Waltz and director of national intelligence Tulsi Gabbard.
In an article titled The Trump Administration Accidentally Texted Me Its War Plans, Mr Goldberg revealed he "knew two hours before the first bombs exploded that the attack might be coming".
He said he had received a connection request on the encrypted messaging service Signal by Mr Waltz on 11 March and was invited to join the "Houthi PC small group" two days later.
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On 15 March US airstrikes killed at least 53 people in Yemen in retaliation for Houthi threats to begin targeting "Israeli" ships after Israel blocked aid entering the Gaza Strip. The daily bombardment has continued for the 10 days since then.
"Your time is up, and your attacks must stop, starting today," Mr Trump said at the time. "If they don't, hell will rain down upon you like nothing you have ever seen before." He said Iran would be held "fully accountable" for its proxy's actions, adding: "And we won't be nice about it!"
When Mr Goldberg initially received a connection request from Mr Waltz he was sceptical and initially thought "someone could be masquerading as Waltz in order to somehow entrap me".
Leak raises huge questions about national security
By David Blevins, Sky correspondent in Washington DC
"FUBAR" - that's one congressman's response to the jaw-dropping news that Trump officials discussed war plans in a group chat on the Signal app.
It's an old military acronym meaning 'F***ed up beyond recognition" or "…beyond repair".
"Only one word for this: FUBAR," said Democrat representative Pat Ryan, an army veteran who sits on the armed services committee.
The leak raises huge questions about national security, but legal experts suggest establishing the group on Signal may violate the espionage act.
A spokesperson for the National Security Council said: "At this time, the message thread that was reported appears to be authentic, and we are reviewing how an inadvertent number was added to the chain.
"The thread is a demonstration of the deep and thoughtful policy coordination between senior officials. The ongoing success of the Houthi operation demonstrates that there were no threats to our servicemembers or our national security."
Responding to the report Mr Trump said "I know nothing about it" and called The Atlantic "not much of a magazine". He added: "I don't know anything about it. You're telling me about it for the first time."
Read more:
Who are the Houthis?
Group included 'active intelligence officer' and references to classified computer systems
After he was added to the "Houthi PC small group" on 13 March, Mr Goldberg saw a message from Mr Waltz asking the other members to provide a point of contact "for us to coordinate with over the next couple of days and over the weekend".
In total 18 people were part of the group, Mr Goldberg said, including Steve Witkoff, Mr Trump's Middle East and Ukraine negotiator, and an "active intelligence officer" whose name he did not publish.
The next day Mr Waltz texted the group: "Team, you should have a statement of conclusions with taskings per the Presidents [sic] guidance this morning in your high side inboxes," with "high side" referring to classified computer systems.
"State and DOD [Department of Defence], we developed suggested notification lists for regional Allies and partners. Joint Staff is sending this am [morning] a more specific sequence of events in the coming days and we will work w DOD to ensure COS [chief of staff], OVP [office of the vice president] and POTUS [president of the United States] are briefed."
'I think we are making a mistake', vice president says
Mr Trump's vice president Mr Vance, who was at an economic event in Michigan, messaged: "I think we are making a mistake.
"[Three] percent of US trade runs through the [Suez Canal]. 40 percent of European trade does. There is a real risk that the public doesn't understand this or why it's necessary. The strongest reason to do this is, as POTUS said, to send a message."
He added: "I am not sure the president is aware how inconsistent this is with his message on Europe right now. There's a further risk that we see a moderate to severe spike in oil prices. I am willing to support the consensus of the team and keep these concerns to myself. But there is a strong argument for delaying this a month, doing the messaging work on why this matters, seeing where the economy is, etc."
European 'free-loading' is 'PATHETIC', senior officials say
Later in the conversation, Mr Waltz criticised the limited capabilities of European navies, writing: "Whether it's now or several weeks from now, it will have to be the United States that reopens these shipping lanes. Per the president's request we are working with DOD and State to determine how to compile the cost associated and levy them on the Europeans."
Mr Vance addressed Mr Trump's defence secretary Mr Hegseth in a message reading: "If you think we should do it let's go. I just hate bailing Europe out again."
Mr Hegseth replied: "VP: I fully share your loathing of European free-loading. It's PATHETIC. But Mike is correct, we are the only ones on the planet (on our side of the ledger) who can do this. Nobody else even close. Question is timing. I feel like now is as good a time as any, given POTUS directive to reopen shipping lanes. I think we should go; but POTUS still retains 24 hours of decision space."
An account believed to be the deputy White House chief of staff, Stephen Miller, then said: "As I heard it, the president was clear: green light, but we soon make clear to Egypt and Europe what we expect in return. We also need to figure out how to enforce such a requirement. EG, if Europe doesn't remunerate, then what? If the US successfully restores freedom of navigation at great cost there needs to be some further economic gain extracted in return."
Messages could 'harm American military and intelligence personnel'
The next day, the day of the strikes, Mr Goldberg said he saw messages which "if they had been read by an adversary of the United States, could conceivably have been used to harm American military and intelligence personnel".
"I will say a prayer for victory," Mr Vance said.
Mr Goldberg said after the strikes many of those in the group celebrated with messages including "good job" and "God bless".
When he realised the messages were real Mr Goldberg removed himself from the Signal group and emailed several officials in the group for comment.
A spokesperson for Mr Vance replied: "The Vice President's first priority is always making sure that the President's advisers are adequately briefing him on the substance of their internal deliberations," he said. "Vice President Vance unequivocally supports this administration's foreign policy. The President and the Vice President have had subsequent conversations about this matter and are in complete agreement."
It comes after Mr Hegseth's office announced a crackdown on leaking sensitive information.