"There have been no requests from other agencies to support at this time, but we're always available to support" the city's police department of other federal agencies, McCarthy said at a press conference.

McCarthy, who has ultimate command of the National Guard in the nation's capital, defended the use of reservist troops during protests against police brutality and racism over the summer.

An inquiry has been launched into the actions of the National Guard during a heavy-handed crowd dispersal operation in Washington in June.

"We don't police America's streets," said McCarthy. "We support law enforcement, whether that is at the federal or state, local levels."

President Donald Trump, who has repeatedly made unsubstantiated warnings that his rival Democrats are plotting election fraud, has called on his supporters to turn up at polling stations and to "protect" ballots, raising fears of clashes if the race turns out to be very close.

On June 1, National Guard helicopters flew very low over anti-racism protesters close to the White House to try to disperse them, ripping the branches off trees and whipping other debris over streets.

The technique was criticized as it is usually only deployed on overseas theaters of combat to break up threatening crowds.

McCarthy said an internal Pentagon investigation into the incident had been wrapped up and the findings sent to the inspector general of the Department of Defense, and that their release was "imminent."

Trump was accused of trying to politicize the military after the Chairman of the Joint Chiefs of Staff, General Mark Milley, and Defense Secretary Mark Esper accompanied him as he walked to a photo op by a church near the White House this summer, just after police had charged protestors to clear the square.

While the Army has been trying to play down any apparent politicization of its role, Trump campaign ads appeared this week showing the president with the two military chiefs at his side.

General Milley let it be known that he had not given his authorization for the use of his image in a political campaign advertisement.