(CNN) Donald Trump is ratcheting up his rhetoric about American Muslims, saying there's precedent for monitoring some mosques amid the recent terror wave.
At a Birmingham, Alabama, rally on Saturday -- which included a physical altercation between a black protester and several white Trump backers -- the 2016 Republican front-runner suggested law enforcement keep an eye on certain Islamic houses of worship which, in his view, could pose terrorist threats.
"I want surveillance of certain mosques if that's OK," Trump told the often-raucous and approving crowd. "We've had it before."
The remarks echo a call Trump made earlier in the week, when he said on MSNBC he'd "strongly consider" shutting down mosques in the U.S.
The billionaire businessman also linked current terrorist concerns, after the Paris carnage and other attacks, with 9/11.
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"I watched the World Trade Center go down," Trump asserted, adding he watched in New Jersey, "as thousands of people were cheering as the building was coming down."
Trump then denounced calls to resettle Syrian refuges on U.S. soil, which his Republican rivals for the nomination also oppose.
"I want surveillance. I will absolutely take (a) database on the people coming in from Syria. "If we can't stop it -- but we are going to if I win -- they're going back."
Several attendees at the rally punched and kicked a protester who tried to disrupt Trump's speech.
At least a half-dozen attendees shoved and tackled the protester, a black man, to the ground as he refused to leave the event. At least one man punched the protester and a woman kicked him while he was on the ground.
All of the attendees who were involved in the physical altercation with the protester were white.
The protester appeared to be shouting "black lives matter" and later removed his sweatshirt to reveal a shirt with those words.
At least one attendee shouted "all lives matter" as the protester was eventually led out by police officers on the scene.
Birmingham Police Lt. Sean Edwards told CNN that three people were asked to leave the event following the scuffle. No arrests were made, and the protester did not require medical attention.
Campaign spokeswoman Hope Hicks told CNN that "the campaign does not condone this behavior."
Trump has fended off criticism recently that he was accused of backing a U.S. database on all Muslims in the country. Trump has denied making that remark but hasn't dismissed the idea out-of-hand.
The database controversy began Thursday when Trump told Yahoo News that he would create new anti-terrorism measures if he's elected.
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"We're going to have to do things that we never did before. And some people are going to be upset about it, but I think that now everybody is feeling that security is going to rule," he told Yahoo News. "And certain things will be done that we never thought would happen in this country in terms of information and learning about the enemy. And so we're going to have to do certain things that were frankly unthinkable a year ago."
The Yahoo reporter asked about the possibility of a database for Muslims or "a form of special identification that noted their religion." Trump did not say no to either idea. Then, after an Iowa campaign event later that day, an NBC reporter asked Trump if he favored a database to track Muslims in the country. Trump responded in a way some took as backing that idea.
At Saturday's rally in Alabama, Trump said he decided not to answer once he heard the reporter identified as being with NBC News.