"Kelly -- and five other members of Congress -- released a reckless and seditious video that was clearly intended to undermine good order and military discipline," Hegseth said in a post on X.

In response to the November video and other statements, the Pentagon opened proceedings that could see Kelly's retired rank reduced, said Hegseth, who has also "issued a formal Letter of Censure, which outlines the totality of Captain (for now) Kelly's reckless misconduct."

The senator from Arizona hit back, saying on X that Hegseth "wants to send the message to every single retired servicemember that if they say something he or Donald Trump doesn't like, they will come after them the same way. It's outrageous and it is wrong."

In the video, six Democratic lawmakers with military or intelligence service backgrounds said the Trump "administration is pitting our uniformed military and intelligence community professionals against American citizens."

"Right now, the threats to our constitution aren't just coming from abroad, but from right here at home," they said, adding: "You can refuse illegal orders."

The lawmakers in the video did not specify which orders they were referring to, but the Trump administration has come under fire for its employment of US forces both at home and abroad.

Inside the United States, Trump has ordered the National Guard into multiple US cities -- often against the wishes of local officials, who have responded with legal challenges -- claiming the deployments are necessary to maintain order against sporadic, sometimes violent protests.

And outside the country, Trump has ordered strikes on a series of alleged drug-smuggling vessels in the Caribbean Sea and eastern Pacific Ocean that have left more than 100 people dead since early September -- actions that experts say amount to extrajudicial killings.