In this file photo taken on February 26, 2022, former US president Donald Trump speaks at the Conservative Political Action Conference in Orlando, Florida (AFP)

The US Justice Department stated in a court filing Thursday that former US President Donald Trump can be sued by police and anyone harmed in the January 6, 2021 attack on the US Capitol by his supporters.

The government stated in an official legal opinion issued to a federal court in Washington that, while a president has absolute immunity for his official activities in the office, he can be sued for acts obviously outside of his official duties.

The decision was presented at the request of the court, which is hearing a lawsuit filed by two police officers and 11 MPs who allege they were injured in the January 6 incident.

Trump, who was sued among other major figures accused of encouraging the attack, which occurred two weeks before he was to depart the White House, claimed total immunity to avoid being sued.

Trump, the Justice Department said, claimed immunity because his pronouncements up to and during the attack amounted to "speech on matters of public concern," which is within his official duties, even if that speech can be seen as inciting violence.

Meanwhile, the Justice Department said the court should dismiss Trump's categorical argument.

"As the nation's leader and head of state, the president has 'an extraordinary power to speak to his fellow citizens and on their behalf,'" the Department said.

"But that traditional function is one of public communication and persuasion, not incitement of imminent private violence," it said.

It noted that a president's campaign speech does not have blanket protection, implying that Trump's support for the January 6 mob – which rejected his loss in the presidential election two months earlier – could fall into that category.

The agency said it was not commenting on the merits of the case, such as whether Trump incited violence or not, but merely that doing so was not covered by his presidential immunity.