US President Donald Trump has committed to an "orderly" transition of power a day after his supporters stormed Congress, provoking world condemnation.

Allowed back on Twitter after a suspension, the Republican president decried the rioters' "heinous attack".

He spoke as top Democrats called for him to be removed from office, just 13 days before he is due to step down.

Mr Trump's remarks were widely seen as his first public acknowledgement of his defeat in November's election.

In November he denied conceding after tweeting about Democratic US President-elect Joe Biden: "He won because the Election was Rigged."

What did Trump say?

Mr Trump returned to Twitter on Thursday evening, following a 12-hour freeze of his account after the social media company said his tweets could stoke violence.

In the new video message, he said: "Now Congress has certified the results a new administration will be inaugurated on January 20th.

"My focus now turns to ensuring a smooth, orderly and seamless transition of power. This moment calls for healing and reconciliation."

He also praised his "wonderful supporters" and promised "our incredible journey is only just beginning".

In the clip he barely touched on his baseless claims of voter fraud that riled up diehard supporters on Wednesday in a rally outside the White House, before they marched to the Capitol and forced their way inside.

The stunning breach of the seat of US government forced Vice-President Mike Pence and lawmakers to be evacuated and postpone for several hours their certification of Mr Biden's victory over Mr Trump.

Who has resigned?

Also on Thursday evening, Education Secretary Betsy DeVos became the second cabinet member to quit following the Capitol riot.

In her resignation letter, DeVos - one of the longest serving members of the president's administration - accused him of fomenting Wednesday's violence.

"There is no mistaking the impact your rhetoric had on the situation, and it is the inflection point for me," she wrote.

Earlier in the day, Transportation Secretary Elaine Chao stepped down, saying she had been "deeply troubled" by the rampage.

Others aides to quit include special envoy Mick Mulvaney, a senior national security official, and the press secretary to First Lady Melania Trump.

A state department adviser was also sacked after calling Mr Trump "unfit for office" in a tweet.

Who's seeking to oust Trump?

The top congressional Democrats, House of Representatives Speaker Nancy Pelosi and Senate Democratic leader Chuck Schumer, are urging Mr Pence and Mr Trump's cabinet to remove the president for "his incitement of insurrection".

"The President's dangerous and seditious acts necessitate his immediate removal from office," they said in a joint statement.

The duo called for Mr Trump to be ousted using the 25th Amendment to the US Constitution, which allows the vice-president to step up if the president is unable to perform his duties owing to a mental or physical illness.

But it would require Mr Pence and at least eight cabinet members to break with Mr Trump and invoke the amendment - something they have so far seemed unlikely to do.

If the vice-president failed to act, Mrs Pelosi indicated she would convene the House to launch the second impeachment proceedings against Mr Trump.

However, the Democrats would need to rely on the support of Republicans to secure the necessary two-thirds majority in the Senate to convict Mr Trump under the articles of impeachment in the constitution, and they would be unlikely to get those numbers.

What was the role of the police?

Law enforcement have been heavily criticised after they were over-run by the protesters.

President-elect Joe Biden said: "Nobody could tell me that if it was a group of Black Lives Matter protesters yesterday they wouldn't have been treated very differently than the thugs that stormed the Capitol."

Images captured inside the Capitol building showed protesters roaming through some of the corridors unimpeded.

However, one officer has been placed on leave after fatally shooting a female demonstrator in the House. Law enforcement told US media she was unarmed.

Washington police say 68 people have so far been arrested, only one of them from the DC area.

The FBI is seeking to identify those involved in the rampage. The Department of Justice says those arrested could face charges of seditious conspiracy, as well as rioting and insurrection.

One of those detained at the Capitol had a "military-style automatic weapon and 11 Molotov cocktails (petrol bombs)", according to the federal attorney for Washington DC.

On Thursday, crews began installing a non-scalable 7ft (2m) fence around the Capitol. It will remain in place for at least 30 days.

The official responsible for security in the House of Representatives, the sergeant at arms, has resigned. Reports say US Capitol Police (USCP) chief Steven Sund is also resigning, effective 16 January, following calls from Ms Pelosi.

Mr Schumer has called for his counterpart in the Senate to be sacked.

Who died?

Four people have been confirmed dead in Wednesday's mayhem.

Ashli Babbitt, a 35-year-old US Air Force veteran from San Diego, California, was named as the woman fatally shot by a police officer.

Three others died after suffering unspecified medical emergencies on Capitol grounds, police said.

They were named on Thursday as Benjamin Phillips, 50, from Pennsylvania; Kevin Greeson, 55, from Alabama; and Rosanne Boyland, 34, from Georgia. Mr Greeson's family said he died of a heart attack.

On Thursday evening, congressman Dean Phillips, a Minnesota Democrat, tweeted that a USCP officer had also died.

But the police department later said the report was inaccurate.

"Although some officers were injured and hospitalized yesterday, no USCP officers have passed away," the statement said.

Police said on Wednesday that 14 police officers had been injured in the riot. One had received "significant facial injuries" after being hit by a projectile. Another also needed hospital treatment after being dragged into a crowd and assaulted.