Trump ordered the deployment -- which follows a similar move during protests in Los Angeles in June -- as part of what he billed as a crackdown on crime in Washington, where violent offenses are in fact down.

"As of today, all 800 Army and Air National Guardsmen are mobilized... as part of Joint Task Force DC, and they are now here in our capital," Pentagon Press Secretary Kingsley Wilson told journalists.

They "will assist the DC Metropolitan Police Department and federal law enforcement partners with monument security, community safety patrols, protecting federal facilities and officers" and traffic control posts, Wilson said.

The troops "will remain until law and order has been restored in the District, as determined by the president," she added.

The US Army later said the National Guard's initial mission "is to provide a visible presence in key public areas, serving as a visible crime deterrent."

"They will not arrest, search, or direct law enforcement," but they "have the authority to temporarily detain individuals to prevent imminent harm," the Army said in a statement.

The troops will be equipped with protective gear, it added, saying that weapons would be available if needed but would remain in the armory.

Trump announced the National Guard deployment -- along with a federal takeover of the city's police department -- on Monday, vowing "to take our capital back."

In a further tightening of control, US Attorney General Pam Bondi signed an order late Thursday granting the head of the federal Drug Enforcement Administration the executive powers of Washington police chief, codifying the federal takeover of the capital's law enforcement.

The city's Democratic mayor Muriel Bowser reacted to Bondi's order in a post on X, in which she said: "We have followed the law... there is no statute that conveys the District's personnel authority to a federal official."

Bowser's post also contained images of a letter from the district's elected attorney general Brian Schwalb to Washington's police chief Pamela Smith.

"It is my opinion that the Bondi Order is unlawful, and that you are not legally obligated to follow it," Schwalb wrote.

The overwhelmingly Democratic US capital faces allegations from Republican politicians that it is overrun by crime, plagued by homelessness and financially mismanaged.

However, data from Washington police shows significant drops in violent crime between 2023 and 2024, although that was coming off the back of a post-pandemic surge.

The deployment of troops in Washington comes after Trump dispatched the National Guard and Marines to quell unrest in Los Angeles, California, that was spurred by immigration enforcement raids.

It was the first time since 1965 that a US president deployed the National Guard against the wishes of a state governor.

Most National Guard forces answer to state governors and have to be "federalized" to be brought under presidential control, but in Washington these troops already report only to the US president.