In a weekend of bad events for his campaign, GOP presidential front-runner Donald Trump continued his run of controversial rhetoric by claiming he witnessed people in Jersey City cheering as the Twin Towers fell during terrorist attacks on September 11, 2001.

See also: Trump is getting pummeled by his political opponents over Muslim database

It began Saturday during a rally in Birmingham, Alabama when Trump called for surveillance of "certain mosques," during a speech in which the candidate suggested a return to waterboarding and continued to pitch his plan for a database to track Syrian refugees within the United States.

Later, talking about security issues, Trump said, according to the New York Times:

“Hey, I watched when the World Trade Center came tumbling down. And I watched in Jersey City, New Jersey, where thousands and thousands of people were cheering as that building was coming down. Thousands of people were cheering. So something’s going on. We’ve got to find out what it is.”

Trump then doubled-down on the claim during a Sunday appearance on ABC's This Week in an interview with 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. 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."

While rumors of such behavior have persisted in certain corners of the Internet since 9/11, there has never been any proof of such events occurring on U.S. soil. The most specific rumors, that such celebrations took place in Patterson, New Jersey, which has a large Muslim population, were later refuted by police and city officials.

And Jersey City Mayor Steve Fulop was quick to come to his city's defense, telling the Star-Ledger, "Trump is plain wrong... Trump needs to understand that Jersey City will not be part of his hate campaign."

New Jersey governor and fellow GOP 2016 candidate Chris Christie, who has been outspoken about his role in his state's 9/11 recovery, responded to Trump's claim Sunday evening, reported Buzzfeed, saying, "I don’t recall that. I don’t. I mean, listen, I can’t say, Matt, I can’t say that I have – it was a pretty emotional time for me because, as I’ve mentioned before, there’s family involved, there’s friends involved and so it was a pretty harrowing time. I do not remember that."

Former New York governor George Pataki, who was governor at the time of the attacks, also responded, via Twitter.

Not sure what luxury spider-hole @realDonaldTrump was hiding in on Sept11 but I saw Americans come together that day @GStephanopoulos — George E. Pataki (@GovernorPataki) November 22, 2015

Mashable has reached out to a Trump campaign spokesperson for comment on Trump's statements as well as to confirm Trump's whereabouts on September 11, 2001.

Trump's campaign also came under the spotlight on Saturday when, prior to his speech at the Birmingham event, attendees were seen roughing up a Black Lives Matter protester who began chanting during the event. The protester, Mercutio Southall, said he was also subjected to racial epithets as he was escorted out.

A black protester at Trump's rally today in Alabama was shoved, tackled, punched & kicked: https://t.co/Aq0wuaAtax pic.twitter.com/cTRDMtjuBl — Jeremy Diamond (@JDiamond1) November 21, 2015

Trump, speaking to Fox News, said of the incident, "Maybe he should have been roughed up because it was absolutely disgusting what he was doing," something of a contradiction to the statement put out by his campaign, which said it did not condone the physicality of the incident.