The warning was made in an internal FBI bulletin obtained and published by CNN and America’s ABC News.

“Armed protests are being planned at all 50 state capitols from 16 January through at least 20 January, and at the US Capitol from 17 January through 20 January,” the bulletin was reported as saying.

“On 8 January, the FBI received information on an identified group calling for others to join them in ‘storming’ state, local and federal government courthouses and administrative buildings in the event POTUS is removed as President prior to Inauguration Day.

“This identified group is also planning to ‘storm’ government offices including in the District of Columbia and in every state, regardless of whether the states certified electoral votes for Biden or Trump, on 20 January.”

The FBI received the information only two days after the violent assault on the US Capitol by Trump supporters seeking to stop Congress from ratifying Biden’s election win.

The FBI also said it knew of “various threats to harm President-Elect Biden ahead of the presidential inauguration”, and that “additional reports indicate threats against VP-Elect Harris and Speaker Pelosi”.

It comes as the National Guard was authorised to send 15,000 troops to Washington, and the US National Parks service shut the Washington Monument to visitors, citing threats of violence in the lead-up to Biden’s swearing-in.

Biden’s inaugural committee said on Monday the theme of the January 20 ceremony would be “America United”.

Trump, who has sought unsuccessfully to overturn the November 3 election results with false claims of widespread fraud, said last week he would not attend the ceremony, a decision the president-elect supported.

Washington Mayor Muriel Bowser called for the US Interior Department to cancel public-gathering permits through January 24.

In a letter to acting Homeland Security Secretary Chad Wolf made public on Sunday, Bowser called for a fresh approach to security after what she called last week’s “unprecedented terrorist attack”.

Bowser asked Wolf to extend the National Special Security Event period from Monday through January 24. The Secret Service heads security operations for events, including presidential inaugurations, considered to be nationally significant.

Wolf said in a statement he had instructed the Secret Service to begin National Special Security Event operations for the inauguration effective Wednesday, instead of January 19 as previously scheduled. The acting secretary told his staff he was stepping down on Monday.

The assault on the Capitol, challenging the certification of Biden’s election victory, sent lawmakers into hiding and left five people dead, including a Capitol Police officer. Dozens of people have been charged in the violence and hundreds of more cases are expected.

The assault occurred shortly after Trump urged supporters to march on the Capitol during a rally where he repeated false claims his resounding defeat in November’s election was illegitimate.

Democrats in Congress began a push on Monday to force Trump from office, introducing an article of impeachment that accuses him of inciting insurrection.

Meanwhile, Trump and Vice-President Mike Pence have spoken for the first time since last week’s Capitol insurrection, during which Pence was forced to flee the Senate chamber and retreat to a secure location.

A senior administration official says the two met Monday evening in the Oval Office.

The official, who spoke on condition of anonymity to discuss the private meeting, said the two had a “good conversation” discussing the week ahead and “reflecting” on the administration’s accomplishments during the past four years.

The official said that during the meeting, both men agreed that “those who broke the law and stormed the Capitol last week do not represent the America first movement backed by 75 million Americans” and pledged to continue working on behalf of the country for the remainder of their term.

The person did not mention Trump’s lingering anger over Pence’s refusal to go along with his unconstitutional scheme to try to overturn the results of the November election that he lost.

Nor did the person mention whether Pence confronted Trump for using him as a scapegoat and tweeting that he lacked courage while the siege was underway.

-with AAP