Former US president Donald Trump has been acquitted on charges of inciting an insurrection at the US Capitol.

A majority of Senate Republicans closed ranks and refused to punish the former president in his historic second impeachment trial.

The five-day trial saw Democratic prosecutors argue, bolstered by dramatic video of the 6 January riot, that Mr Trump betrayed his oath by whipping up his supporters into storming Congress in a last-ditch attempt to cling to power.

It concluded as expected with a majority of Republicans declaring him not guilty, in a sign of the powerful grip the 74-year-old continues to exert on his party.

But while the 57-43 majority that voted to convict fell short of the two-thirds needed in the Senate, seven Republicans joined with Democrats to seek Mr Trump's conviction, making it the most bipartisan impeachment trial in US history.

US President Joe Biden said that despite the acquittal the charges against Mr Trump are "not in dispute" and called on Americans to defend democracy.

Mr Trump, who has been secluded in his Florida club since leaving office on 20 January, welcomed the verdict, denouncing the proceedings as "yet another phase of the greatest witch-hunt in the history of our country".

Despite the stain of a second impeachment, Mr Trump hinted at a possible political future, saying that "our historic, patriotic and beautiful movement to Make America Great Again has only just begun".

"We have so much work ahead of us, and soon we will emerge with a vision for a bright, radiant, and limitless American future," he said in a statement.

Mr Trump was impeached by the House of Representatives on 13 January, a week after the chaotic assault that stunned the nation and provoked widespread bipartisan outrage.

Democrats argued that Mr Trump's behavior was an "open and shut" case of impeachable conduct, retracing how he spent two months repeating the falsehood that the election was stolen, before inciting his supporters to attack Congress and stop the certification of Mr Biden's victory.

"He summoned his supporters to Washington... whipped them into a frenzy, and directed them at the Capitol," Senate Majority Leader Chuck Schumer said after the vote.

The defence team swatted the evidence away, arguing that Mr Trump's appeal to supporters to "fight like hell, at the rally that preceded the attack", was merely rhetorical.

But their central argument was that the Senate had no constitutional jurisdiction to try a former president. Most Republican senators agreed.

'Practically and morally responsible'

But Mitch McConnell, the powerful Senate minority leader who voted to acquit on those grounds, left no doubt he blames Mr Trump for the riot, which sent politricians fleeing for safety as a marauding mob rampaged through the Capitol.

The former Trump ally unleashed a searing rebuke of the ex-president, calling his actions preceding the assault a "disgraceful dereliction" of duty.

"There's no question -- none -- that president Trump is practically and morally responsible for provoking the events of the day," Mr McConnell told the chamber after the vote.

He stressed that while Congress has exhausted its avenues for punishing Mr Trump, the US justice system has not.

"President Trump is still liable for everything he did while he was in office," Mr McConnell said. "He didn't get away with anything yet."

In a statement, Mr Biden said that "while the final vote did not lead to a conviction, the substance of the charge is not in dispute" and acknowledged Mr McConnell's critique of Mr Trump.

"This sad chapter in our history has reminded us that democracy is fragile. That it must always be defended. That we must be ever vigilant," Mr Biden said.

Building their case over two days, Democratic impeachment managers described how Mr Trump first encouraged, then refused to call a halt to the 6 January insurrection that left then-vice president Mike Pence and politicians in mortal danger.

Proclaiming Mr Trump's innocence, defence lawyer Michael van der Veen told the Senate that "the act of incitement never happened" and that rioters acted alone.

Read more: Predictable outcome to impeachment trial but with last-minute twist

After the trial, House Speaker Nancy Pelosi, who was openly targeted by rioters and evacuated from the Capitol on 6 January, laid into the "cowardly" Republican senators who voted to acquit.

"Senate Republicans' refusal to hold Trump accountable for igniting a violent insurrection to cling to power will go down as one of the darkest days and most dishonorable acts in our nation's history," she said in a statement.

A furious Ms Pelosi later belittled the prospect that Mr Trump might now be the subject of a censure vote in Congress.

"These cowardly senators who couldn't face up to what the president did and what was at stake for our country are now going to have a chance to give a little slap on the wrist?" she said to reporters, making that gesture.

"We censure people for using stationery for the wrong purpose. We don't censure people for inciting insurrection that kills people in the Capitol," she said.

Before moving to final arguments, the proceedings were interrupted for a few hours when House impeachment managers, in a surprise move, said they wanted to call witnesses.

But they backed down, instead reaching agreement with the defense that a statement by congresswoman Jamie Herrera Beutler would be entered as evidence.

Lead impeachment manager Jamie Raskin had wanted Ms Herrera Beutler, a Republican who voted to impeach Mr Trump last month, to testify over her statement that Republican House Minority Leader Kevin McCarthy made a frantic call to Trump during the attack and implored him to call off the rioters.

She said Mr McCarthy briefed her about the call, and said that when he told a sceptical Mr Trump that the insurrectionists were his supporters, "according to McCarthy, the president said: 'Well, Kevin, I guess these people are more upset about the election than you are'."