US President Donald Trump has accused six Democratic lawmakers of "seditious behaviour, punishable by death", after they released a video urging US service members to refuse unlawful commands.

"This is really bad, and Dangerous to our Country. Their words cannot be allowed to stand. SEDITIOUS BEHAVIOR FROM TRAITORS!!! LOCK THEM UP???," Trump wrote on social media.

The six lawmakers, all of whom have served in the military or intelligence community, called Trump's remarks dangerous and said they amounted to threats against elected officials.

"No threat, intimidation, or call for violence will deter us from that sacred obligation," they said in a joint statement.

The video by Democrats, which was shared by Michigan Senator Elissa Slotkin, features Arizona Senator Mark Kelly and Representatives Chris DeLuzio of Pennsylvania, Maggie Goodlander of New Hampshire, Chrissy Houlahan of Pennsylvania and Jason Crow of Colorado.

Sen Kelly, who served in the Navy and is a former astronaut, says: "Our laws are clear. You can refuse illegal orders."

"No one has to carry out orders that violate the law or our constitution," the lawmakers say in the video.

"This administration is pitting our uniformed military and intelligence community professionals against American citizens," it says. "Like us, you all swore an oath to protect and defend this Constitution. Right now, the threats coming to our Constitution aren't just coming from abroad but from right here at home."

The response from Trump on Thursday morning came in a series of posts on Truth Social.

"It's called SEDITIOUS BEHAVIOR AT THE HIGHEST LEVEL. Each one of these traitors to our Country should be ARRESTED AND PUT ON TRIAL. Their words cannot be allowed to stand — We won't have a Country anymore!!! An example MUST BE SET," he wrote in one post on Thursday.

He went on to say: "This is really bad, and Dangerous to our Country. Their words cannot be allowed to stand. SEDITIOUS BEHAVIOR FROM TRAITORS!!! LOCK THEM UP???"

In a third post, he wrote: "SEDITIOUS BEHAVIOR, punishable by DEATH!"

Trump also reposted a TruthSocial post that read "HANG THEM GEORGE WASHINGTON WOULD !!"

At a press briefing on Thursday, White House press secretary Karoline Leavitt rejected suggestions that Trump was calling for the execution of members of Congress.

"Many in this room want to talk about the president's response, but not what brought the president to responding in this way," she said, accusing the lawmakers of encouraging military personnel to defy "lawful orders".

Heightened concern over US political rhetoric

Leavitt quickly responded "no" when asked at a White House press briefing on Thursday afternoon whether Trump wants to "execute" members of Congress, saying the media should instead focus on the lawmakers' own comments.

"They are literally saying to 1.3 million active duty service members to defy the chain of command, not to follow lawful orders," Leavitt said at Thursday's press briefing.

"It perhaps is punishable by law," she added later.

Leadership in the US House of Representatives have said they are working with Capitol Police to adequately protect the lawmakers - and their families - who are at the centre of Trumps' posts.

Democratic House Minority Leader Hakeem Jeffries slammed Trump's remarks, saying the president must "recant his violent rhetoric before he gets someone killed".

Republican House Speaker Mike Johnson, however, defended the president, saying Trump was simply "defining the crime of sedition" calling the Democrats' video "wildly inappropriate" and "very dangerous".

The Department of Justice and Pentagon will be reviewing the matter, he said.

Trump's remarks come amid heightened concern about politically motivated attacks in the US.

An October Pew Research Center study found 85% of Americans believe such violence is increasing, a trend echoed in a November Politico and Public First poll.

Trump, himself, was targeted in two alleged assassination attempts - one at a political rally during his presidential campaign last year that left one person dead. Trump and several others in attendance were injured.

Just this year there have been a number of high-profile incidents, including the assassination of conservative commentator Charlie Kirk, an arson attack on Democratic Pennsylvania Governor Josh Shapiro's home, and the killing of a Democratic Minnesota lawmaker and her husband.

In the wake of Kirk's murder, many conservatives including Trump spoke out against Democrats and said they were responsible for the growing political violence in the US.

Republican Congresswoman Marjorie Taylor Greene recently spoke out about the increased number of threats she's received since breaking with Trump on some policies. Their feud boiled over last week when Trump posted several times about her, calling her "wacky" and a "traitor". Her son also received a death threat, according to local police.

More public officials are reporting swatting - making prank calls to emergency services to deploy a Special Weapons and Tactics team (Swat) - attempts in recent months.

That includes an Indiana Republican who was the focus of a separate Truth Social attack from the president, over his stance on redistricting in the state. (BBC)