The Pentagon had been criticized for its slow response during the January 6 attack on Congress by supporters of then-president Donald Trump, which left five people dead and dozens injured.

It took military officials more than three hours to get the National Guard deployed to Congress as it was being besieged by rioters because of a chain of bureaucratic requirements.

The Secretary of Defense will from now on be "the single approval authority for all requests" for emergency use of District of Columbia National Guard personnel inside Washington, the Pentagon said.

"By clarifying and refining the request process... the Department will be able to respond to requests efficiently, quickly, and effectively," Pentagon spokesman John Kirby said in a statement.

The US capital, which is separate from the bordering states of Maryland and Virginia and is not a state in its own right, has a special status, preventing local officials from sending military, police or National Guard forces to the US Capitol, which is a federal building.

Asked to provide help when Capitol police were being overwhelmed by rioters, Pentagon officials later said that they were reluctant to send uniformed and armed reservists to Congress for fear of exacerbating tensions.

Hundreds of National Guard reservists stationed in Washington over the previous summer during huge anti-racism protests had been criticized for violence toward demonstrators.