Arizona senator Mark Kelly has ridiculed comments made by Donald Trump, who called his recent actions "seditious" in a furious Truth Social post.

The president had also implied Democrats calling on military personnel to reject illegal orders be "executed", with Kelly addressing the comments on Jimmy Kimmel Live. Secretary of War Pete Hegseth confirmed an investigation was now underway into Kelly over "potentially unlawful comments", The Guardian reported.

In response to Trump's "seditious behaviour" comment, Kelly suggested the president is using the FBI against him and a select group of Senators who called on the military to oppose illegal orders as a "tool to intimidate and harass members of Congress".

Kelly went further in his comments during an appearance on Jimmy Kimmel's talk show, where he called the comment made by Trump "ridiculous".

Kimmel asked Kelly "what even is sedition?", to which the Arizona senator replied, "Well this is the investigation, because of what Donald Trump said. From what I can tell, and I don't know Pete Hegseth well, I sit on the committee that ultimately had to confirm him, so I know a little bit about his background. He's totally unqualified.

"From what I can tell, talking to some of my Republican colleagues, I mean he just wants to please the president. This is what he can do this week, he can go after me under the uniform code of military justice, which is a law in the military, which is kind of wild because we recited something in the uniform code of military justice and he's going to prosecute me under the uniform code of military justice."

Kelly would go on to call Hegseth's decision to prosecute him "so ridiculous", adding, "It's almost like you can't make this s**t up." It comes as a former Bush administration official calls the Trump administration on its bluff to prosecute Kelly.

Kelly had participated in a video published last week in which several Democratic lawmakers urged active duty service members to defy unlawful orders, a video that sparked outrage from President Donald Trump, who went on to accuse the lawmakers of “seditious behavior” and threatened to execute them.

On Monday, the Pentagon announced that it was investigating Kelly – a former Navy pilot – for his participation in the video, but on Tuesday, Cully Stimson – also a former Navy pilot – poured cold water on the prosecution’s chances at success.

Stimson said, "I don't think any military jury is ever going to convict this guy, ever. So I think the punishment here is the process, and they'll ultimately not prosecute him or bring him back on active duty."