On Monday President Trump declared a state of emergency for Washington DC until 24 January, which enables the Department of Homeland Security (DHS) to act to "avert the threat of a catastrophe".
Chad Wolf, acting head of the DHS, said he had instructed the US Secret Service to begin operations for the inauguration on Wednesday - six days early - "in light of events of the past week and the evolving security landscape".
Later on Monday, Mr Wolf became the third Trump cabinet secretary to step down since the riots, after Betsy DeVos and Elaine Chao.
Mr Wolf said his departure had been prompted by "recent events", including court rulings challenging the legal validity of his appointment.

US security officials have warned of possible armed protests being held across the country in the days before Joe Biden is sworn in as president.
There are reports of armed groups planning to gather at all 50 state capitols and in Washington DC in the run-up to his 20 January inauguration.
Security plans are being tightened for the event, which will happen two weeks after a pro-Trump mob stormed Congress.
House Democrats say a vote to impeach the president will happen on Wednesday.
They accuse President Trump of "incitement of insurrection" and say the vote will be held unless Vice-President Mike Pence invokes constitutional powers to remove Mr Trump from office. There is no sign Mr Pence is prepared to do so.
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