NATIONAL Guard units patrolling the US capital Washington DC at the direction of President Donald Trump have started carrying firearms.

President Trump has also indicated his willingness to use the military in other, mainly black, cities in the US.

A Defence Department official, who was not authorised to speak publicly, said that some units on certain missions would be armed — some with handguns and others with rifles.

The spokesperson said that all units with firearms have been trained and are operating under strict rules for use of force.

A statement from the joint task force that has taken over policing in the nation’s capital said that units began carrying their service weapons on Sunday and that the military’s rules say force should be used “only as a last resort and solely in response to an imminent threat of death or serious bodily harm.”

The defence official said that only troops on certain missions would carry guns, and that would include those patrolling to establish a law enforcement presence throughout the capital.

Thousands of National Guard and federal law enforcement officers are now patrolling the capital’s streets, drawing sporadic protests from local residents.

The development in Trump’s extraordinary effort to override the law enforcement authority of state and local governments comes as he is considering expanding the deployments to other Democratic-led cities, including Baltimore, Chicago and New York.

Earlier on Sunday, the president responded to an offer by Maryland’s governor to join him in a tour of Baltimore by saying he might instead “send in the ‘troops’.”

Governor Wes Moore, a Democrat, has criticised Mr Trump’s unprecedented flex of federal power.

President Trump has said that Chicago and New York are most likely his next targets, eliciting strong pushback from Democratic leaders in both cities.

The Washington Post reported on Saturday that the Pentagon has spent weeks preparing for an operation in Chicago that would include National Guard troops and potentially active-duty forces.

US police are routinely armed, and shoot dead about 1,000 people a year on average.