WASHINGTON — North Korean state television aired video on Thursday from the historic summit between President Donald Trump and Kim Jong Un that included a surprising moment when the American president saluted a North Korean general.

Trump reached out to shake the general's hand, and the general responded with a salute. Trump reciprocated, saluting the general back before the men shook hands.

The video is now running over and over on North Korean state television with an enthusiastic anchor track.

Social media exploded with outrage about Trump's salute.

Retired Army Maj. Gen. Paul Eaton, a senior adviser to the advocacy group VoteVets.org, said, "It is wholly inappropriate for the commander in chief of our armed forces to salute the military of our adversary, especially one which is responsible for a regime of terror, murder and unspeakable horror against its own people."

Col. Jack Jacobs, a Medal of Honor recipient and an NBC News analyst, said that the North Korean general's salute was a sign of respect but Trump's salute "seemed like a reflexive action."

"If I had been his military aide I would have told him, 'They're going to salute you, but don't return the salute, just move smartly down the line.'"

Presidential historian Michael Beschloss told NBC News that "one test of a leader is that he knows what message a public gesture sends. In this case, either he made a mistake or he was trying to send the message that he doesn't take the human rights abuses by the North Korean military as seriously as many other Americans do."

In the military a salute is a sign of respect, with a junior officer or junior enlisted service member always saluting first.

While civilians do not return a salute from a military member, the President is the Commander in Chief and will generally return a salute from U.S. military service members but not military from other nations.

In 2009 during his first visit to Japan as president, Barack Obama bowed deeply from the waist when greeting Japanese Emperor Akihito, eliciting criticism from conservatives who said the gesture projected weakness on the world stage.

Trump was quick to criticize Obama a few years later when he bowed during a greeting of Saudi King Abdullah in 2012. "@BarackObama bowed to Saudi king in public — yet the Dems are questioning @MittRomney's diplomatic skills," Trump tweeted.

The Amateur! First @BarackObama was caught bowing to the Saudi King but now the President of Mexico! http://t.co/f0CFiUS9 — Donald J. Trump (@realDonaldTrump) June 20, 2012

A salute is a sacred element of military service and history. U.S. military members are taught the salute originated in Roman times when knights in armor would raise their visors with their right hand when greeting a fellow knight.

According to a New York Times story from 2009, Ronald Reagan was thought to be the first president to begin returning salutes regularly. He had sought advice from the commandant of the Marine Corps, who told him that as commander in chief he could salute anyone he liked.

In September 2014 Obama saluted with a cup of coffee in his hand, drawing criticism from conservatives and retired military who deemed it the latte salute and displayed it as a evidence that Obama lacked understanding about the military.

Asked about the salute by NBC News, White House spokesman Hogan Gidley said he hadn’t seen the video, "so it’s tough for me to comment on that."

The White House did not immediately respond to an additional request for comment.