The National Guard is preparing to deploy at least 20,000 troops in Washington DC for the January 20 swearing-in of US President-elect Joe Biden.
The city's acting police chief, Robert Contee, announced the figure on Wednesday.
One police officer and four protesters died in the siege.
About 8,000 National Guard troops were on hand for Mr. Trump's 2016 inauguration.
Roads near the Capitol, which were overrun with violent protesters on January 6, have also been closed.
The National Park Service has closed the Washington Monument to tours and Mayor Muriel Bowser has asked visitors to stay away.