Donald Trump has come again under fire after mocking a New York Times reporter with a congenital joint condition during a campaign rally in South Carolina this week.

The incident occurred as the Republican presidential hopeful was defending his recent claim that he had witnessed thousands of Muslims cheering in New Jersey on September 11, 2001, as the World Trade Center collapsed.

The assertion has since been fact-checked and discredited by law enforcement and government officials who were in New Jersey in the days and weeks following the terrorist attacks.

On November 24, Donald Trump berated New York Times investigative reporter Serge Kovaleski for his recent recollection of an article he had written a few days after the attacks.

Donald Trump appeared to mock Serge Kovaleski’s physical condition; the reporter has arthrogryposis, which visibly limits flexibility in his arms.

“Now, the poor guy – you’ve got to see this guy, <<Ah, I don’t know what I said! I don’t remember!>>” Donald Trump said as he jerked his arms in front of his body.

The gesture was all the more personal because Serge Kovaleski covered Donald Trump while reporting for the New York Daily News between 1987 and 1993, a tumultuous period for the businessman in which he struggled through several financial setbacks.

“The sad part about it is, it didn’t in the slightest bit jar or surprise me that Donald Trump would do something this low-rent, given his track record,” Serge Kovaleski said.

Donald Trump campaign spokeswoman Hope Hicks declined to comment on the record about the incident. A campaign official speaking on background said Donald Trump was “not aware of any condition and was not mocking his physical appearance in any way”.

In his speech on November 24, Donald Trump defended his recollection of the Muslim revelers by citing a 2001 article by Serge Kovaleski, who worked for The Washington Post at the time, noting that “authorities detained and questioned a number of people who were allegedly seen celebrating the attacks and holding tailgate-style parties on rooftops while they watched the devastation on the other side of the river”.

Those allegations were never corroborated but have persisted in online rumors in the 14 years since the attacks. In an interview on CNN this week, Serge Kovaleski said he did not recall “anyone saying there were thousands, or even hundreds, of people celebrating”.

Serge Kovaleski’s friends and colleagues took to social media this week to defend him – and excoriate Donald Trump.

The New York Times also issued a sharply worded statement November 25, saying: “We think it’s outrageous that he would ridicule the appearance of one of our reporters.”

On the same day, Donald Trump tweeted: “The failing @nytimes should be focused on good reporting and the papers financial survival and not with constant hits on Donald Trump!”