The Anti-Defamation League (ADL) on Sunday criticized Republican presidential contender Donald Trump for his comments that thousands of Arab Americans cheered as the Twin Towers fell on 9/11.

On Saturday and Sunday, Trump said he observed "thousands and thousands" of Arab people in New Jersey "cheering as the World Trade Center came down" — an online conspiracy debunked by police and media.

"It was well covered at the time," he told ABC on Sunday. "There were people over in New Jersey that were watching it, a heavy Arab population that were cheering as the buildings came down. Not good."

In a statement to BuzzFeed News, the Anti-Defamation League (ADL), an international NGO that monitors anti-Semitism, said: "It is unfortunate that Donald Trump is giving new life to long-debunked conspiracy theories about 9/11."

"This seems a variation of the anti-Semitic myth that a group of Israelis were seen celebrating as the Twin Towers fell," the ADL said.

"His comments are irresponsible — not to mention factually challenged."