The National Guard has been mobilized to Washington ahead of pro-Trump demonstrations planned this week as Congress convenes to certify the election results.
The Guard will be used to help control crowds and manage traffic, the police chief said. Mayor Muriel Bowser requested the Guard be activated and urged residents and others to stay safe and be cautious.
"We're asking D.C. residents and people who live in the region to avoid confrontations with anybody who's looking for a fight," Bowser said. "And the best way to do that is to avoid the area."
Congress is scheduled to meet Wednesday to formally count the Electoral College votes. President Donald Trump lost the election but has baselessly alleged fraud. On Tuesday, Georgia will hold runoff elections that will determine which party controls the Senate.
Organizers plan to rally Tuesday evening at Freedom Plaza and all day Wednesday on the Ellipse, including a 1 p.m. Wednesday march to the Capitol, The Associated Press reported.
Trump has encouraged the rally, and on Sunday tweeted "I will be there. Historic day!" while retweeting a message about Wednesday's planned event.
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More than 300 District of Columbia National Guard personnel will support the city government Tuesday and Wednesday, providing crowd control at Metro stations and helping with street closures, the guard said in a statement.
Maj. Gen. William J. Walker, commanding general of the D.C. National Guard, said they would be in a support role.
Acting Metropolitan Police Department Chief Robert Contee warned demonstrators and anyone else that guns are not permitted.
"We have received some information that there are individuals intent on bringing firearms into our city, and that just will not be tolerated," Contee said.
In December, several people were stabbed during clashes around a pro-Trump rally.
A leader of the Proud Boys, Enrique Tarrio, was arrested Monday after entering Washington after being accused of burning a Black Lives Matter sign that had been torn down at a historic Black church during that Dec. 12 rally. He also allegedly had two high-capacity magazines, police said.