Footage of President Trump saluting a top North Korean general during this week’s summit meeting with the North’s leader, Kim Jong-un, set off debate on Thursday over military and diplomatic protocol.

The scene was part of a 42-minute documentary that aired on state television two days after the two leaders met in Singapore, offering another window into the historic encounter.

While greeting North Korean dignitaries after his initial handshake with Mr. Kim, Mr. Trump proceeded down the line shaking hands, the video shows. When Mr. Trump offered his hand to Gen. No Kwang-chol, who was recently promoted to defense chief, the general saluted instead.

Mr. Trump quickly raised his own hand and saluted back.

Maj. Gen. Paul Eaton, a retired United States Army general, criticized the gesture in a statement.