All 800 National Guard troops who were ordered to the US capital Washington to aid law enforcement personnel by US President Donald Trump have now been mobilised, the Pentagon said on Thursday.

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 the capital, where violent offences are in fact down.

"As of today, all 800 Army and Air National Guardsmen are mobilised... 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.

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."

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 "federalised" to be brought under presidential control, but in Washington these troops already report only to the US president. (AFP)