All 50 US states and the District of Columbia (DC) are on alert for possible violent protests this weekend, ahead of President-elect Joe Biden’s inauguration on Wednesday.
The FBI has warned of possible armed marches by pro-Trump supporters at all 50 state capitols.
National Guard troops have been sent en masse to Washington DC, to deter any repeat of last week’s deadly riots.
Much of Washington DC will be locked down ahead of Wednesday’s inauguration, with National Guard troops deploying in their thousands.
Many streets – some miles from the Capitol, the site of deadly rioting on 6 January – have been blocked off with concrete barriers and metal fences.
The National Mall, which is usually thronged with thousands of people for inaugurations, has been shut at the request of the Secret Service – the agency charged with protecting the president.
The Biden team had already asked Americans to avoid travelling to the nation’s capital for the inauguration because of the Covid-19 pandemic. Local officials said people should watch the event remotely.
Sunday is expected to also be a particular focus for protests, after posts on pro-Trump and far-right online networks called for armed demonstrations on that day.
Some militias have told their followers not to attend, however, citing heavy security or claiming the planned events are police traps.
The tough security measures follow a week in which Donald Trump became the first US president to be impeached twice. He now faces a Senate trial, on a charge of “incitement of insurrection” linked to the storming of the US Capitol by groups of his supporters. They did so in a bid to thwart Congress certifying Joe Biden’s victory in the presidential election.
Dozens of arrests have been made in relation to the assault on the Capitol building.
Meanwhile, the Biden team has set out plans to reverse key Trump policies.
In the hours after Mr Biden sets foot in the White House, he will embark on a blitz of executive actions designed to signal a clean break from his predecessor’s administration, according to a memo seen by US media. Among them include: return to the Paris climate agreement, repeal the controversial travel ban on Muslim-majority countries and make wearing masks mandatory .