In a rare joint message, the U.S. military’s Joint Chiefs of Staff on Tuesday assailed last week’s riots at the U.S. Capitol – which led to five deaths, including a Capitol Police officer – as an assault on the nation’s constitutional process.

The message marked the first public comments on the riot from Chairman of the Joint Chiefs of Staff General Mark Milley.

"The violent riot in Washington D.C. on January 6, 2021 was a direct assault on the U.S. Congress, the Capitol building, and our Constitutional process," read an internal memo to troops obtained by Reuters.

A member of the military stands guard outside Russell Senate Office Building on Capitol Hill in Washington, Friday, Jan. 8, 2021, in response to supporters of President Donald Trump who stormed the U.S. Capitol. 

A member of the military stands guard outside Russell Senate Office Building on Capitol Hill in Washington, Friday, Jan. 8, 2021, in response to supporters of President Donald Trump who stormed the U.S. Capitol.  (AP)

The memo reminded troops that freedom of speech and assembly does "not give anyone the right to resort to violence, sedition and insurrection."

Milley was in the headlines last summer when he expressed regret for accompanying President Donald Trump during a photo-op at Lafayette Square amid protests, calling the decision "a mistake."

The incident came at the height of nationwide protests against police and law enforcement, sparked by the police killing of George Floyd in Minneapolis.

Tuesday’s memo from the military’s top leaders comes amid fears of renewed violence on Inauguration Day. Signed by all members of the Joint Chiefs of Staff, the memo reminded military members that Joe Biden was duly elected as the next president and will be sworn into office on Jan. 20.

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It also comes as law enforcement agencies attempt to determine the full extent of criminal activity at the Capitol and to discover the extent of participation by current or past military members.

Some military veterans did participate in the riots, but the extent of any active-duty involvement has not been established. Sen. Tammy Duckworth, an Iraq war veteran, on Monday wrote to the Defense Department requesting that it cooperate with the FBI and the U.S. Capitol Police in investigating whether current and retired members of the armed forces were part of a "seditious conspiracy" against the government.

The Joint Chiefs memo did not allude directly to the question of military involvement.

"We witnessed actions inside the Capitol building that were inconsistent with the rule of law," the memo said. "The rights of freedom of speech and assembly do not give anyone the right to resort to violence, sedition and insurrection.

"As service members, we must embody the values and ideals of the nation. We support and defend the Constitution. Any act to disrupt the Constitutional process is not only against our traditions, values and oath; it is against the law."

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Ahead of next week's inauguration and President Donald Trump's departure from office, the National Guard is gearing up to provide support to law enforcement agencies. There is no plan to use active-duty forces in security operations.

The Associated Press contributed to this report.