The White House has confirmed that a journalist seems to have been inadvertently added to a group chat in which US national security officials discussed plans for a strike against the Houthi rebel group.
"At this time, the message thread that was reported appears to be authentic," Brian Hughes, a spokesman for the National Security Council, said in a statement to the BBC.
"We are reviewing how an inadvertent number was added to the chain.
Editor-in-chief of the Atlantic Jeffrey Goldberg said he received an invite on the encrypted messaging app Signal from an account purporting to be White House National Security Adviser Michael Waltz on March 11, four days before the US launched what it described as a "decisive and powerful" series of air strikes against the Houthis in Yemen.
Also in the chat, Goldberg reported, were accounts that matched the names of Vice-President JD Vance, Defence Secretary Pete Hegseth and Director of the Central Intelligence Agency (CIA) John Ratcliffe.
Goldberg said he watched as the group chat discussed targets and timings for military strikes. And those plans appeared accurate when US later launched air strikes on Houthis in Yemen that matched details from the group chat.
He said top officials from various agencies also appeared to be added.
"The thread is a demonstration of the deep and thoughtful policy co-ordination between senior officials," Hughes said.
Signal is used by journalists and Washington officials because of the secure nature of its communications, the ability to create aliases, and send disappearing messages.
"This is blatantly illegal and dangerous beyond belief," Democratic Senator Elizabeth Warren says of the group chat breach. "Our national security is in the hands of complete amateurs," she said on social media.
"What other highly sensitive national security conversations are happening over group chat? Any other random people accidentally added to those, too?"
Republican Alaska Senator Lisa Murkowski said: "Think about what we would do if Biden were president and this came out... we would raise the roof", according to a reporter for Semafor, external.
"It's going to be interesting to see if anybody loses their job over this," she added.
Democratic Senator Mazie Hirono posted: "Egregious, reckless, and illegal. No amount of spin can change that."