The United Nations has said it has solved the mystery of why an escalator abruptly stopped shortly after US President Donald Trump stepped onto it, suggesting his videographer may have accidentally triggered a safety mechanism.

Trump jokingly complained about the incident during his speech to world leaders earlier in the day after his teleprompter also malfunctioned.

"These are the two things I got from the United Nations — a bad escalator and a bad teleprompter," he told the 193-member assembly, drawing some laughter.

However, White House Press Secretary Karoline Leavitt took a harder line.

"If someone at the UN intentionally stopped the escalator as the President and First Lady were stepping on, they need to be fired and investigated immediately," she posted on X.

UN spokesperson Stephane Dujarric later explained that a readout of the escalator's central processing unit showed it "had stopped after a built-in safety mechanism on the comb step was triggered at the top of the escalator."

He said Trump’s videographer had been walking backwards up the escalator to film the president’s arrival with First Lady Melania Trump.

"The videographer may have inadvertently triggered the safety function," Dujarric said in a statement.

"The safety mechanism is designed to prevent people or objects accidentally being caught and stuck in or pulled into the gearing."

The White House did not immediately respond to a request for comment on the UN findings.

On the teleprompter, Trump told the General Assembly: "I can only say that whoever's operating this teleprompter is in big trouble."

But a UN official later clarified that the White House had operated its own teleprompter during the speech.

After Trump concluded, UN General Assembly President Annalena Baerbock remarked: "The UN teleprompters are working perfectly."