Trump jokingly complained about the incident during his speech to world leaders earlier on Tuesday after the teleprompter also didn't work.
"These are the two things I got from the United Nations - a bad escalator and a bad teleprompter," he told the 193-member assembly, to some laughter.
However, White House Press Secretary Karoline Leavitt wasn't so lighthearted about it.
"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 after the incident.
UN spokesperson Stephane Dujarric said a readout of the escalator's central processing unit indicated 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 travelling backwards up the escalator to capture his 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."
However, a UN official said the White House had operated its own teleprompter.
After Trump finished speaking, UN General Assembly President Annalena Baerbock said: "The UN teleprompters are working perfectly".
