A Jewish group in calling Donald Trump’s assertion that thousands of Arab-Americans cheered on 9/11 “irresponsible” and “factually challenged.”

The presidential hopeful made the statement at a rally in Birmingham, Alabama on Saturday, telling an applauding crowd that “thousands and thousands” of the “large Arab populations” of New Jersey cheered when the World Trade Center was brought down by a terror plot in 2001.

The GOP frontrunner reaffirmed his comments Sunday in a phone conversation with ABC’s George Stephanopoulos.

“There were people that were cheering on the other side of New Jersey, where you have large Arab populations. They were cheering as the World Trade Center came down,” Trump said. “I know it might be not politically correct for you to talk about it, but there were people cheering as that building came down — as those buildings came down. And that tells you something. It was well-covered at the time.”

Jewish advocacy group the Anti-Defamation League (ADL) told BuzzFeed News Sunday, “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.”

The New York Times reports that a rumor circulating following the attacks–that Muslims were celebrating in New Jersey–was soon debunked by police.