US President Donald Trump has defended the top adviser who inadvertently looped a magazine editor into a war group chat, saying he'd "learned a lesson" from the "glitch".
Michael Waltz, who leads the White House's National Security Council, added the journalist to a group on the messaging app Signal, where officials discussed a planned military operation in Yemen earlier this month.
The embarrassing error has triggered widespread concern in Washington about the sharing of confidential information, and particularly raised red flags about the use of a commercial app to share potentially classified material.
But Mr Trump told NBC News: "Michael Waltz has learned a lesson, and he's a good man."
He described the error as "the only glitch in two months, and it turned out not to be a serious one", as it had "no impact at all" on the "perfectly successful" military operation.
Asked how the journalist was added to the chat, Mr Trump said: "It was one of Michael's people on the phone. A staffer had his number on there."
Later, when asked about the incident before a meeting of newly appointed ambassadors, Mr Trump said Mr Waltz had been unfairly attacked over it.
"I don't think he should apologise," Mr Trump said.
"I think he's doing his best. It's equipment and technology that's not perfect, and probably he won't be using it again, at least not in the very near future."
He said he had asked Mr Waltz to look into the app's use. Mr Waltz, who was at the meeting said:
"Yes, sir, we are. We have our technical experts looking at it, we have our legal teams looking at it, and of course, we're going to keep everything as secure as possible."
He said he had never communicated with the journalist, Atlantic editor-in-chief Jeffrey Goldberg. "We are looking into and reviewing how the heck he got into this room."
Senators have meanwhile used a congressional committee hearing to question two of the officials named as part of the group chat.
Director of National Intelligence Tulsi Gabbard and CIA Director John Ratcliffe both insisted before the Senate Intelligence Committee that no classified information was shared.
But some senators pushed back. "It's hard for me to believe that targets and timing and weapons would not have been classified," said independent senator Angus King, who caucuses with the Democratic Party.
Mr Ratcliffe said the Signal app had been used permissibly and legally, "at least to my understanding", but senators appeared frustrated as he repeatedly answered "I don't recall" when asked about what was discussed.
He disputed a suggestion the incident was a "huge mistake", prompting Democratic Senator Jon Ossoff to say:
"This is utterly unprofessional. There's been no apology, no recognition of the gravity of this error.
"And by the way, we will get the full transcript of this chain and your testimony will be measured carefully against its content."
Ms Gabbard refused to discuss specifics such as whether she used her personal phone or government-issued device to participate in the chat.
"I won't speak to this because it's under review by the National Security Council," she said. "Once that review is complete, I'm sure we'll share the results with the committee."
Democratic Senator Mark Warner, the committee's vice-chairman, said a military or intelligence officer who had made the same error would be fired.
He said it was just the latest in a string of dangerous White House decisions, which ranged from cutting foreign aid to security programs, to firing staff overseeing America's nuclear weapons stockpile.
Such decisions were damaging trust with allies such as the Five Eyes nations, he said. The Fives Eyes is comprised of Australia, New Zealand, Canada, the UK and the US.
"Things like the Five Eyes are based on trust built on decades, but so often that trust is now breaking literally overnight," Senator Warner said.
The White House has responded to the story with a public relations offensive, attacking the editor who was included in the chat and describing the coverage as a "coordinated effort to distract" from Mr Trump's successes.
"Jeffrey Goldberg is well-known for his sensationalist spin," Trump spokeswoman Karoline Leavitt posted online, adding that "no war plans were discussed".
Her comments echoed those made earlier by Defence Secretary Pete Hegseth, who labelled Goldberg a "deceitful and highly discredited so-called journalist".
Goldberg has defended the report.
"He [Hegseth] was texting attack plans — when targets were going to be targeted; how they were going to be targeted; who was at the targets; when the next sequence of attacks was happening," he told CNN.
