The Democrat lawmakers who encouraged US troops to disobey illegal orders are pushing back on an alleged federal inquiry into their actions.

Democratic Senator Elissa Slotkin of Michigan said the FBI on Monday notified the six lawmakers who appeared in last week's video of the investigation.

"No amount of intimidation or harassment will ever stop us from doing our jobs and honoring our Constitution," four US House members said.

Their message to troops prompted US President Trump to accuse the Democrats of "seditious behavior, punishable by death" and a Pentagon review of "serious allegations of misconduct" against Democratic Senator Mark Kelly of Arizona, who also appeared in the video.

The Department of Justice and declined to comment on the alleged investigation.

Reuters reported on Tuesday that a Justice Department official, who spoke on condition of anonymity, said the FBI has requested interviews with six Democratic politicians to determine "if there's any wrongdoing, and then go from there".

The video by Democrats, all of whom have served in the military or intelligence community, was shared last week by Slotkin and features Kelly and US Representatives Chris Deluzio, Maggie Goodlander, Chrissy Houlahan and Jason Crow.

The message came amid escalating tensions between the Trump administration and the Venezuelan government, as well as Democrat-led cities opposing Trump's deployment of National Guard troops there.

Slotkin said on Tuesday that the FBI's counterterrorism unit sent a note to the Congress members to notify them of an alleged inquiry into the lawmakers.

"The President's reaction and the use of the FBI against us is exactly why we made the video," she said at an event in Michigan.

"He believes in using the federal government against his perceived adversaries, and he's not afraid to use the arms of the government against people he disagrees with," she said, describing Trump's actions as "a scare tactic".

Likewise, US representatives Deluzio, Goodlander, Houlahan and Crow said that Trump is using the FBI as "tool to intimidate and harass" members of Congress, confirming that the FBI contacted the House and Senate Sergeants at Arms to request interviews.

"We swore an oath to support and defend the Constitution of the United States. That oath lasts a lifetime, and we intend to keep it. We will not be bullied. We will never give up the ship," they said.

The video - in which Kelly accused the administration of "pitting our uniformed military and intelligence community professionals against American citizens" - drew Trump's ire and he suggested on social media that they be arrested, locked up and hanged.

His words drew bipartisan condemnation and the president ultimately walked back his remarks in a Fox News interview, clarifying that he was "not threatening death".

On Monday, the Pentagon accused Senator Kelly, a former captain in the US Navy and astronaut, of breaching military law. The defence department said it would conduct a review to determine whether the Arizona lawmaker should be recalled to active duty to face court-martial proceedings.

Even though Kelly retired from the military, he is still subject to the Uniform Code of Military Justice (UCMJ) - a federal law enacted by Congress in 1951 that subjects members of the military to a special set of rules.

Defence secretary Pete Hegseth accused Kelly of violating the UCMJ and of using his rank and service affiliation as a way to lend "the appearance of authority to his words" in the video.

He added that Kelly's conduct "brings discredit upon the armed forces and will be addressed appropriately".

But Kelly also pushed back, saying that he has "given too much to this country to be silenced by bullies who care more about their own power than protecting the Constitution".

On Tuesday, the Department of Defense appeared to formalise its review of Kelly's conduct.

The department posted an image on social media showing a signed memo from Hegseth to the secretary of the US Navy regarding Kelly's "potentially unlawful comments" in the 18 November video, referring the matter to the Navy for review.

While the intelligence community does not have a code comparable to the UCMJ, Liz Lyons, a spokeswoman for the Central Intelligence Agency, on Tuesday reminded former officers of the oath they took and commitment they made while serving in the intelligence community.

Former officers should "conduct themselves accordingly - even long after they leave", she wrote on X.

Lyons said the assertion by Slotkin - a former CIA analyst - that CIA officers are receiving illegal orders and should therefore refuse to follow them "is now, by her own admission, without basis and recklessly false".

Fox News reported on Tuesday that the FBI and Department of Justice contacted Capitol Police to schedule interviews with the six members of Congress.

The FBI declined to comment on Tuesday when contacted by the BBC. (BBC)

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