US Transport Secretary Elaine Chao said Thursday she is resigning over the storming of the Capitol by President Donald Trump's supporters, the highest level White House resignation yet in the wake of the violence.

Chao, who is married to Republican Senate Majority Leader Mitch McConnell, said it was "a traumatic and entirely avoidable event as supporters of the President stormed the Capitol building following a rally he addressed."

"It has deeply troubled me in a way I simply cannot set aside," she added.

Earlier Thursday, former chief of staff Mick Mulvaney said he was quitting his diplomatic post to protest the mob violence, which Trump encouraged in a bid to overturn his election loss to Democrat Joe Biden.

"I can't stay here, not after yesterday. You can't look at that yesterday and think I want to be a part of that in any way, shape or form," Mulvaney told CNBC television.

Mulvaney, who had been moved from chief of staff to special envoy for Northern Ireland, said he informed Secretary of State Mike Pompeo of his resignation.

"I can't do it. I can't stay," he told CNBC, indicating that other White House staff were eying the exits.

"Those who choose to stay, and I have talked with some of them, are choosing to stay because they’re worried the president might put someone worse in," he said.

Immediately after Wednesday's violence, which Trump has yet to condemn, deputy national security adviser Matt Pottinger resigned.

Another departure was Stephanie Grisham, a former White House press secretary now working as spokeswoman for First Lady Melania Trump.

US media reported that Marc Short, chief of staff to Vice President Mike Pence, had been blocked from entering the White House -- apparently in retaliation for Pence's decision to ignore Trump's demand that he block the certification of Biden.

In another sign of upheaval at the White House, Trump on Thursday withdrew his nomination of Chad Wolf for the permanent job at the head of the Department of Homeland Security, where he is now in acting capacity.

This came just after Wolf said he found the action by Trump's supporters in the halls of Congress "sickening" and urged the president to "strongly condemn" the violence.

The outrage across Washington at the day's events is feeding growing speculation that more senior Trump administration figures may be leaving.

Biden will take over the presidency when he is sworn in on January 20.