US National Guard defend Washington round the clock – in pictures

Up to 15,000 Guard members are expected to be on duty in the build-up to the inauguration of president-elect Joe Biden

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  Hundreds of US National Guard troops rest in the Capitol Visitors Center, with the Statue of Freedom seen at center, on Capitol Hill in Washington, DC, USA. EPA

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  Members of the National Guard take a rest in the Rotunda of the US Capitol in Washington, DC. AFP

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  Members of the National Guard rest in the Capitol Visitors Center on Capitol Hill in Washington, DC. AFP

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  House Majority Leader Steny Hoyer, Democrat of Maryland, walks past members of the National Guard as he arrives at the US Capitol in Washington, DC. AFP

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  Members of the National Guard take a rest in the Rotunda of the US Capitol in Washington, DC. AFP

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  U.S. National Guard riot shields are laid out at the ready outside the U.S. Capitol Building on Capitol Hill in Washington, U.S. REUTERS

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  U.S. National Guard riot shields are laid out at the ready outside the U.S. Capitol Building on Capitol Hill in Washington. REUTERS

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  Hundreds of US National Guard troops rest in the Capitol Visitors Center on Capitol Hill in Washington, DC, USA. EPA

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  epa08935276 Hundreds of US National Guard troops rest in the Capitol Visitors Center on Capitol Hill in Washington, DC, USA, 13 January 2021. At least ten thousand troops of the National Guard will be deployed in Washington by the end of the week, with the possibility of five thousand more, to help secure the Capitol area ahead of more potentially violent unrest in the days leading up to the Inauguration of US President-elect Joe Biden. Democrats are attempting to impeach US President Donald J. Trump after he incited a mob of his supporters to riot on the US Capitol in an attempt to thwart Congress from certifying Biden's election victory. EPA/MICHAEL REYNOLDS

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  Hundreds of US National Guard troops rest in the Capitol Visitors Center on Capitol Hill in Washington, DC, USA. EPA

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  Hundreds of US National Guard troops rest in the Capitol Visitors Center on Capitol Hill in Washington, DC, USA. EPA

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  Members of the National Guard rest in the U.S. Capitol in Washington, DC. Security has been increased throughout Washington following the breach of the U.S. Capitol last Wednesday, and leading up to the Presidential inauguration. AFP

As the US House of Representatives opened its impeachment hearing on Wednesday, the District of Columbia National Guard said it was authorised to arm troops assigned to security duty on US Capitol grounds.

The Guard said the authorisation was requested by federal authorities and approved by Army Secretary Ryan McCarthy about 6pm on Tuesday.

Up to 15,000 Guard members are expected to be on duty in the coming days to support law enforcement in connection with the inauguration of president-elect Joe Biden on January 20.

Authorities are concerned about threats of violence, after the insurrection at the Capitol last week.

The Pentagon's top generals condemned the January 6 attack by supporters of President Donald Trump on Tuesday, telling US troops that it was an illegal assault on the constitutional process.

"The violent riot was a direct assault on the US Congress, the Capitol building and our constitutional process," said a memorandum signed by all eight members of the Joint Chiefs of Staff, led by the chairman, Gen Mark Milley.

"The rights of freedom of speech and assembly do not give anyone the right to resort to violence, sedition and insurrection."

The letter said members of the armed services were bound to defend the constitution.

"Any act to disrupt the constitutional process is not only against our traditions, values and oath; it is against the law," it said.