City officials in Washington have warned supporters of President Donald Trump not to bring guns to protests this week against congressional certification of his election defeat.
Hundreds of National Guard troops have been enlisted to help keep order.
"We have received some information that there are individuals intent on bringing firearms into our city and that just will not be tolerated," Police Chief Robert Contee told a City Hall news conference on Monday.
He added that anyone found doing so or provoking violence would be arrested.
More than 300 troops will be on hand to support the city government, providing crowd control and aiding fire and rescue services, the DC National Guard said in a statement.
They will be joined by the US Capitol Police, US Park Police and US Secret Service, Contee said.
District laws forbid open carry of weapons or possession of a handgun without a local license.
Thousands of Trump supporters, including some far-right nationalist groups that openly carry arms at protests elsewhere, are expected to converge on the capital starting on Tuesday to oppose Congress' certification the next day of his November 3 election loss.
Contee said the protests could be bigger than November and December rallies marred by stabbings and brawls as hundreds of Proud Boys, a group of self-described "Western chauvinists," and other Trump loyalists clashed with counter-protesters, and sought fights with antifa and Black Lives Matter activists.
Trump summoned supporters to this week's gatherings, saying on Twitter on Sunday "I will be there" and on Friday that "it will be wild".
Several rallies are planned for Wednesday, including one outside the US Congress. The White House has not provided details on Trump's appearance.
Congress is constitutionally mandated to certify the presidential election results on Wednesday, in what would normally be a formality overseen by Vice President Mike Pence.
But at least 12 Republican senators and some 140 Republican House of Representatives members have pledged to vote against certification of Biden's win.
The head of the Proud Boys pledged on social media that "record numbers" of members would attend, suggesting they may dress in all black like antifa activists.
"We will be incognito and we will spread across downtown DC in smaller teams," wrote Enrique Tarrio.
Australian Associated Press