US Defense Secretary Lloyd Austin has put 100 National Guard troops on stand-by to help police protect the Capitol if needed, the Pentagon says, ahead of a planned rally supporting people charged with taking part in the January 6 riot.
Hundreds of demonstrators are expected in Washington DC on Saturday for the Justice For J6 rally aimed at supporting what they call the "political prisoners" of the January storming of the US Capitol by backers of Donald Trump in a bid to stop certification of President Joe Biden's election victory.
About 60 people are being held behind bars of the more than 600 charged in the deadly riot.
Police are preparing for the possibility that some demonstrators on Saturday may arrive with weapons.
Hundreds of counter-demonstrators are also expected with the possibility of clashes.
A Pentagon spokesman said the request had been made by the Capitol police and the troops would be based out of the DC Armory.
They would be used after local, state and federal law enforcement capabilities had been tapped, the spokesman said.
"The task force will only be deployed upon request of the Capitol Police to help protect the US Capitol Building and Congressional Office buildings by manning building entry points and verifying credentials of individuals seeking access to the building," the spokesman said.
Police have ramped up security around the Capitol, mindful of the rioters on January 6 who attacked police, smashed windows and climbed into the building, sending lawmakers and then-vice president Mike Pence running for safety.
At least 30 of the suspects are jailed in Washington DC while the rest are locked up in facilities across the country.
They have said they are being treated unfairly and one defendant said he was beaten.
Some jailed defendants are charged with assaulting police officers, others with making violent threats.
A few were freed after their arrests but subsequently detained again, accused of violating release conditions.
The US Court of Appeals for the District of Columbia Circuit has set standards for judges to apply in deciding whether to jail a Capitol riot defendant.
A three-judge panel of the appeals court ruled in March that rioters accused of assaulting officers, breaking through windows, doors and barricades or playing leadership roles in the attack were in "a different category of dangerousness" than those who merely cheered on the violence or entered the building after it was breached.
Workers have reassembled a fence that was put up around the white-domed Capitol following the riot but was taken down in July.
The fencing separated the lawns of the Capitol grounds from other government landmarks including the Supreme Court, the Library of Congress, congressional office buildings and the Capitol Reflecting Pool just west of Capitol Hill, where protesters were scheduled to gather on Saturday.
Travellers arriving at the airport nearest Washington DC will face increased security in the run-up to the rally, the Transportation Security Administration has said.
Police and congressional leaders have said they are prepared for Saturday's protest.
Most members of Congress will be out of town.
Australian Associated Press