WASHINGTON (REUTERS, BLOOMBERG) - White House deputy national security adviser Matt Pottinger has resigned, joining a number of officials who are leaving the administration of US President Donald Trump following the storming of Capitol Hill by his supporters.

Mr Mick Mulvaney, former White House chief of staff to the President, also said on Thursday that he is resigning from his current post as special envoy to Northern Ireland. His resignation comes alongside that of Mr Ryan Tully, Mr Trump's top White House adviser on Russia.

Mr Pottinger, a leading figure in the development of Mr Trump's China policy, resigned on Wednesday (Jan 6) in response to Mr Trump's reaction to a mob of protesters who breached the US Capitol, a senior administration official told Reuters. Bloomberg first reported the resignation.

Mr Pottinger's boss, national security adviser Robert O'Brien, has no plans to quit, the official said.

"A strong national security team remains in place at the State Department, the Department of Defence, Treasury, the intelligence community and the National Security Council."

The official said the team has been making sure there are no foreign threats to the United States before the incoming administration of President-elect Joe Biden, who will be inaugurated on Jan 20. The team has been coordinating with Mr Biden's transition team for several weeks.

A senior administration official also told Reuters that more senior members of the National Security Council are expected to step down soon. Speaking on condition of anonymity, the official also said Mr Trump's pledge to an "orderly transition" to Mr Biden was partly intended to head off further resignations but was not likely to stop some departures.

The White House had no immediate comment. Mr O'Brien had asked Mr Pottinger to stay on past Election Day to facilitate the transition to Mr Biden's new team, the official said.

"Pottinger completed those tasks," the person said.

An administration official described Mr Trump as "increasingly isolated" and said that "national security officials who are loyal to their oath to the Constitution will be standing watch until Inauguration Day and will then turn over power to the duly elected new president."

Meanwhile, Mr Mulvaney said he left his job in protest of Wednesday's attack on the Capitol. "I quit because it is the only thing I could do - officially - to express my disapproval of what happened yesterday," Mulvaney told Bloomberg News.

Mr Mulvaney earlier told CNBC that he called Secretary of State Michael Pompeo and resigned after a violent mob stormed the Capitol and disrupted the counting of Electoral College votes. "I can't do it. I can't stay," he said.

"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," Mr Mulvaney added.

In November, Mr Mulvaney had a rosier view of the end of Mr Trump's tenure. In an op-ed published in the Wall Street Journal, Mr Mulvaney predicted Mr Trump would leave office gracefully.

"The President will fight like a gladiator until the election is conclusively determined," he wrote before the race was called.

But, he continued, once a winner is determined, "I have every expectation that Mr Trump will be, act and speak like a great president should - win or lose."

Four people died during the chaos - one from gunshot wounds and three from medical emergencies - after hundreds of Trump supporters stormed the Capitol in a bid to overturn his election defeat to Democrat Biden.

In a video posted to Twitter while the rioters roamed the Capitol, Mr Trump called the protesters "special" and repeated his false claims about election fraud, although he urged protesters to leave.

The melee delayed the certification process of Mr Biden's victory for hours.

Two top aides to First Lady Melania Trump also resigned on Wednesday. Ms Stephanie Grisham resigned as chief of staff to the First Lady.

"It has been an honour to serve the country in the White House. I am very proud to have been a part of Mrs Trump's mission to help children everywhere, and proud of the many accomplishments of this administration," Ms Grisham said in a statement.

Ms Grisham, who spent a year as White House press secretary before becoming chief of staff to the First Lady, did not say whether her resignation was in reaction to the violence, but a source familiar with her decision said it was the last straw.

The White House social secretary Rickie Niceta also resigned, as did a deputy White House press secretary Sarah Matthews, two sources told Reuters.

There was also talk inside the White House that deputy chief of staff Chris Liddell might resign, a source said.

Mr Pottinger, a former Reuters and Wall Street Journal reporter who left journalism to join the US Marines after the Sept 11 attacks on the US in 2001, had served in the White House since the beginning of Mr Trump's presidency in 2017.

The departure of the fluent Mandarin speaker comes at a time of high tension with Beijing.

Mr Trump's administration has pursued hard-line policies towards China on issues ranging from trade to espionage and the coronavirus and relations plummeted to their worst level in decades when the president ramped up rhetoric in his unsuccessful re-election campaign.

Early on Thursday, Mr Pompeo said Washington was considering sanctions and other restrictions on those involved in the arrest of over 50 people, including American lawyer John Clancey, in a new Chinese crackdown in Hong Kong hours before Wednesday's events in Washington.

Mr Pompeo warned that Washington could target Hong Kong's economic and trade office in the US, and in a move likely to further rile Beijing, announced that US Ambassador to the United Nations Kelly Craft would visit Chinese-claimed Taiwan - which is not a UN member due to China's objections.

US lawmakers called the action by Mr Trump's supporters an embarrassment to American democracy that would play into the hands of rivals like China.

"I think they're high-fiving in Beijing," Republican Senator Marco Rubio, a China hawk, told Mr Tucker Carlson on the Fox News channel. "It kind of bolsters their claim that we're falling apart and they're the country of the future."

On Wednesday, China's Washington embassy issued an advisory warning Chinese citizens to strengthen safety precautions in the light of the "large-scale demonstration" in the US capital and a curfew announced by the local government.