The Pentagon chief allegedly included details on the strikes in the private chat -- the second time he has been accused of sharing sensitive military information on the commercial messaging app with unauthorized people.

"This is what the media does. They take anonymous sources from disgruntled former employees and then they try to slash and burn people and ruin their reputations," Hegseth said at the White House, adding: "Not going to work with me."

Hegseth is facing increasing criticism, with three ex-staffers penning a statement decrying their dismissals and his own former Pentagon press secretary all but calling for him to be removed.

Multiple Democratic lawmakers have said it is time for Hegseth, a former Fox News host and army veteran with no previous experience of government or politics, to go.

"Trump's Defense Secretary Pete Hegseth has now leaked classified military plans TWICE -- this time through a unsecured Signal chat on a personal device to friends and family. He's a walking national security disaster and needs to resign or be fired," said Representative Jim McGovern.

Senators Mark Warner, Andy Kim and Elissa Slotkin all called for Hegseth to quit, with the latter saying: "Our military and our country deserve serious leaders. If he cared about the institution he's leading, he should man up, acknowledge he's a distraction to the military's mission, and resign."

But the White House on Monday backed him, with Press Secretary Karoline Leavitt saying that "the president absolutely has confidence in Secretary Hegseth. I spoke to him about it this morning, and he stands behind him."

- 'Total chaos' -

Last month, The Atlantic magazine revealed that its editor-in-chief was inadvertently included in a Signal chat in which officials including Hegseth and National Security Advisor Mike Waltz discussed the March 15 Yemen strikes.

The revelation sparked an uproar, with President Donald Trump's administration forced on the defensive over the leak. A Pentagon inspector general's probe into Hegseth's use of Signal is ongoing.

The New York Times and CNN then reported Sunday that Hegseth had shared information in a second Signal group chat on the same strikes.

The information shared included the flight schedules for warplanes targeting Yemen's Huthi rebels, the Times reported.

The chat included his wife Jennifer, who is a journalist and former Fox News producer, as well as his brother Phil and lawyer Tim Parlatore, both of whom serve in roles at the Pentagon, the newspaper and the channel said, citing anonymous sources.

The reported release of military information in the chat follows other turmoil at the top of the Pentagon, with three senior officials removed last week amid an investigation into alleged leaks.

Former senior advisors Darin Selnick, Dan Caldwell and Colin Carroll hit back on Sunday, saying Pentagon officials had "slandered our character with baseless attacks."

"We still have not been told what exactly we were investigated for, if there is still an active investigation, or if there was even a real investigation of 'leaks' to begin with," they said in a joint statement posted on social media.

Hegseth's former Pentagon press secretary John Ullyot also took aim at him in a scathing opinion piece on Sunday that described "a month of total chaos at the Pentagon."

"President Donald Trump has a strong record of holding his top officials to account. Given that, it's hard to see Defense Secretary Pete Hegseth remaining in his role for much longer," wrote Ullyot.