FBI warns of nationwide armed protests

The FBI has warned of armed protests being planned for Washington and all 50 US state capitals in the run-up to President-elect Joe Biden's January 20 inauguration, a federal law enforcement source says.

Threatened with more violence from outgoing President Donald Trump's supporters following last Wednesday's storming of the US Capitol, the FBI issued warnings for next weekend that run at least until Inauguration Day, the source says.

In other steps to safeguard the US capital, the National Guard was authorised to send up to 15,000 troops to Washington, and tourists were barred from visiting the Washington Monument until January 24.

The chief of the National Guard Bureau, General Daniel Hokanson, told reporters he expected about 10,000 troops in Washington by Saturday to help provide security, logistics and communications.

He said the number could rise to 15,000 if requested by local authorities.

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.

The Park Service said it would suspend tours of the Washington Monument due to safety concerns from threats to disrupt the inauguration.

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.

The presidential inaugural committee and Bowser have told Americans not to travel to the inauguration, and said Washington's National Mall would be covered with 191,500 flags of different sizes, to represent the missing crowds.