Donald Trump's supporters stormed the Capitol on 6 January 2020. [Source: BBC News]

A Trump tweet mobilised far-right extremists to converge on Washington DC on the day of last year’s Capitol riot, a congressional inquiry has heard.

He posted the tweet after “the craziest meeting of the Trump presidency”, said a lawmaker on the panel.

The then-president forged ahead with a rallying call to supporters even though aides repeatedly told him he had fairly lost the 2020 election to Joe Biden.

The committee accuses Mr Trump of an attempted coup to remain in power.

Supporters of Donald Trump violently stormed Congress on 6 January 2021 as lawmakers met to certify Mr Biden’s victory.

Hours before the hearing, Mr Trump, a Republican, dismissed the Democratic-led House of Representatives panel as “Political Hacks and Thugs” perpetrating a “HOAX”.

The select committee has been conducting a nearly year-long investigation into the attack on the Capitol. Tuesday’s session focused on a tweet Mr Trump sent in the early hours of 19 December 2020, and a stormy six-hour meeting at the White House that preceded the post.

Jamie Raskin, a Maryland Democrat who led the hearing, said the meeting had been described as “unhinged” and “not normal”.

Mr Trump had already been told by White House aides and figures within his own campaign team that he should concede to Mr Biden, a Democrat.

However, on 18 December he welcomed to the White House some informal advisers who had been urging him to pursue his unfounded claims of widespread voter fraud.

The group – which included his personal lawyer Rudy Giuliani and his ex-National Security Adviser Michael Flynn – had offered Mr Trump a prewritten executive order meant to allow the seizure of voting machines.

The meeting was intercepted by aides, as well as then-White House counsel Pat Cipollone, who told the committee he was “not happy to see the people”.

“I don’t think any of these people were providing the president good advice,” he added, in recorded testimony to the select committee.

What followed was hours of argument, during which Mr Cipollone said he was attacked “verbally”, but kept “pushing back”, asking the group: “Where is the evidence?” They did not offer any proof, he and other aides told the committee.

The meeting ended after midnight with the idea of seizing ballot boxes rejected. Mr Trump’s tweet sent at 01:42 local time told supporters: “Statistically impossible to have lost the 2020 Election. Big protest in D.C. on January 6th. Be there, will be wild.”

The post, Mr Raskin argued, “electrified and galvanised his supporters”, who believed Mr Trump’s claims that the election had been stolen from him.

The panel says the tweet was the siren call to extremist groups such as the Oath Keepers and Proud Boys to turn up. Two members of the groups are awaiting trial on rare seditious conspiracy charges related to the Capitol riot.

Committee members are trying to draw a direct line between the social media post and the violence on 6 January.

An anonymous Twitter employee told the committee they saw a rise in violent rhetoric online following the tweet. Mr Raskin said some of the responses turned “openly homicidal”.