Democratic lawmakers swiftly blasted the misstep saying it was a breach of U.S. national security and a violation of law that must be investigated by Congress.

The Atlantic's editor-in-chief Jeffrey Goldberg said in a report on Monday that he was unexpectedly invited on March 13 to an encrypted chat group on the Signal messaging app called the "Houthi PC small group." In the group, national security adviser Mike Waltz tasked his deputy Alex Wong with setting up a "tiger team" to coordinate U.S. action against the Houthis.

National Security Council spokesperson Brian Hughes said the chat group appeared to be authentic.

U.S. President Donald Trump launched an ongoing campaign of large-scale military strikes against Yemen's Houthis on March 15 over the group's attacks against Red Sea shipping, and he has warned Iran, the Houthis' main backer, that it needed to immediately halt support for the group.

Hours before those attacks started, Defense Secretary Pete Hegseth posted operational details about the plan in the messaging group, "including information about targets, weapons the U.S. would be deploying, and attack sequencing," Goldberg said. His report omitted the details but Goldberg termed it a "shockingly reckless" use of Signal chat.

Accounts that appeared to represent Vice President JD Vance, U.S. Secretary of State Marco Rubio, CIA Director John Ratcliffe, Director of National Intelligence Tulsi Gabbard, Treasury Secretary Scott Bessent, White House chief of staff Susie Wiles, and senior National Security Council officials were assembled in the chat group, Goldberg wrote.

Joe Kent, Trump's nominee for National Counterterrorism Center director, was apparently on the Signal chain despite not yet being Senate-confirmed.

Trump told reporters at the White House that he was unaware of the incident. "I don't know anything about it. I'm not a big fan of The Atlantic," Trump said. A White House official said later that an investigation was under way and Trump had been briefed on it.

The NSC's Hughes said in a statement: "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."

'EUROPEAN FREE-LOADING'

According to screenshots of the chat reported by The Atlantic, officials in the group debated whether the U.S. should carry out the strikes, and at one point Vance appeared to question whether U.S. allies in Europe, more exposed to shipping disruption in the region, deserved U.S. help.

"@PeteHegseth if you think we should do it let's go," a person identified as Vance wrote. "I just hate bailing Europe out again," the person wrote, adding: "Let's just make sure our messaging is tight here."

A person identified as Hegseth replied: "VP: I fully share your loathing of European free-loading. It's PATHETIC."

Under U.S. law, it can be a crime to mishandle, misuse or abuse classified information, though it is unclear whether those provisions might have been breached in this case. Messages that The Atlantic report said were set by Waltz to disappear from the Signal app after a period of time also raise questions about possible violations of federal recordkeeping laws.

As part of a Trump administration effort to chase down leaks by officials to journalists unrelated to the Signal group, Gabbard posted on X on March 14 that any "unauthorized release of classified information is a violation of the law and will be treated as such."

On Tuesday, Gabbard is due to testify before the Senate Intelligence Committee on worldwide threats to the United States.

Created by the entrepreneur Moxie Marlinspike, Signal has gone from an exotic messaging app used by privacy-conscious dissidents to the unofficial whisper network of Washington officialdom.

Democratic lawmakers called the use of the Signal group illegal and demanded an investigation.

"This is one of the most stunning breaches of military intelligence that I have read about in a very, very long time," Senate Democratic Leader Chuck Schumer said, adding that he would ask Majority Leader John Thune to investigate.

"We're just finding out about it. But obviously, we've got to run it to ground and figure out what went on there. We'll have a plan," Thune, a Republican from South Dakota, said.

There was no immediate suggestion from the White House that the breach would lead to any staffing changes.

"President Trump continues to have the utmost confidence in his national security team, including national security adviser Mike Waltz," White House spokeswoman Karoline Leavitt told Reuters.

Democratic Senator Elizabeth Warren said on X the use of Signal to discuss highly sensitive national security issues was "blatantly illegal and dangerous beyond belief."

"Every single one of the government officials on this text chain have now committed a crime – even if accidentally – that would normally involve a jail sentence," Democratic Senator Chris Coons said on X.