Republican lawmakers have publicly called for Trump to more vocally condemn the violence and to call to an end to the occupation.

Four people have died on the US Capitol grounds and 52 people have been arrested after supporters of President Donald Trump stormed the Capitol in an unprecedented effort to stop Congress from certifying President-elect Joe Biden's election victory.

In a late-night news conference, Metropolitan Police Department Chief Robert J Contee said that 47 of the 52 arrests to date were related to violations of Mayor Muriel Bowser's 6 pm (23GMT) curfew, with 26 of those involving people arrested on US Capitol grounds.

Several others were arrested on charges related to carrying unlicensed or prohibited firearms.

In addition, Contee said, two pipe bombs were recovered from the headquarters of the Republican and Democratic national committees, as well as a cooler from a vehicle on US Capitol grounds that contained Molotov cocktails.

Contee declined to identify the woman, reportedly a dedicated Donald Trump backer and air force veteran, a Capitol Police officer shot and killed, saying next of kin notification was still pending.

Three other people died on Wednesday because of medical emergencies, he added.

The White House says National Guard troops along with other federal protective services stepped in to the Capitol to help end a violent occupation by Trump’s supporters who are seeking to prevent the certification of the 2020 presidential election.

He has refused to concede and has worked over the last two months to convince his supporters that widespread voter fraud prevented his own victory.

The storming of the chamber

The demonstrations flared as lawmakers met inside to formally certify Biden's victory over Trump in the November 3 election. 

Law enforcement authorities struggled to maintain order.

The Senate and the House of Representatives, which were weighing objections to Biden's victory brought by a band of pro-Trump Republican lawmakers, abruptly and unexpectedly recessed.

Protesters barged inside the Senate chamber. One got up on the dais and yelled "Trump won that election."

Several dozen roamed through the halls, yelling, "Where are they?"

Some were also in the visitors' galleries.

A number of Republicans from both chambers had said they will challenge the certification of a handful of states in a last-ditch attempt to either negate Biden's win or delay the certification of his victory.

Other Republicans have said the effort is misguided and could damage the nation over the long-run. 

They have urged the quick certification to clear the way for Biden to be sworn in as president on January 20. 

Any challenge is expected to be rejected by the full House and Senate. 

Pence won't stop Biden win certification

Meanwhile, US Vice President Mike Pence, in defiance of President Trump, said that he will not intervene to stop the certification by Congress of Biden's victory.

"The Constitution constrains me from claiming unilateral authority to determine which electoral votes should be counted and which should not," Pence said in a statement released as a joint session of Congress began to certify the electoral college votes from the November 3 election.

The statement was released as Trump urged Pence at a rally in Washington to decline to certify the results.

READ MORE: Trump vows not to concede as Congress prepares to certify Biden's win

Two top officials resign

Two top aides to first lady Melania Trump resigned with more top White House officials were considering stepping down, including national security adviser Robert O'Brien and his deputy, Matthew Pottinger, sources familiar with the matter said.

Stephanie Grisham resigned as chief of staff to the first lady after Trump supporters occupied the US Capitol.

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 in the nation's capital, but a source familiar with her decision said the violence was the last straw for her.

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

Republican US Senator Lindsey Graham signalled breaking ranks with Trump.

Speaking on the Senate floor during a joint session of Congress, Graham, one of Trump's hitherto staunchest allies, said he and the president "had a hell of a journey."

"I hate it being this way. Oh my God I hate it," he said in animated remarks after Congress reconvened after being stormed by Trump's supporters. "All I can say is 'count me out. Enough is enough. I've tried to be helpful.'"

O'Brien was also considering resigning, as was Pottinger, the deputy national security adviser who has been a key voice on China policy within the administration, two sources said.

"I just spoke with Vice President Pence," O'Brien said in a statement earlier Wednesday, adding, "I am proud to serve with him."

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

The White House declined to comment.

Senate rejects challenge to certifying Biden

The US Senate overwhelmingly rejected the objection by some Republican lawmakers to certifying Arizona's electoral vote for Joe Biden.

The lawmakers voted 93 to 6 against the effort to reject Arizona's electoral count, overcoming the first of what may be multiple hurdles to the November presidential election's certification.

The House of Representatives will also vote on Arizona, and the effort is expected to fail there too, before Congress continues its process to certify the electoral votes of all 50 states.

READ MORE: Warnock wins first Georgia run-off as Dems inch towards Senate control

Trump slams 'weak' Republicans

Earlier, President Trump took aim at Republican members of Congress who have refused to join him in his effort to contest the results of the November election.

Trump told a large crowd of supporters gathered on the Ellipse that they needed to vote these Republicans out of office by putting up challengers in primary elections to push them out. 

"If they don't fight, we have to primary the hell out of the ones that don't fight," Trump said, calling the Republicans who aren't siding with him "weak."

He named and praised Republicans who have pledged to contest the electoral votes of some states on Capitol Hill. 

His supporters, who braved chilly, windy conditions, chanted "Fight for Trump!"

Source: TRTWorld and agencies