The rally in Salt Lake City, coming one week after clashes between supporters and protesters forced Trump to cancel a Chicago event
, was also marked by a couple hundred protesters outside the Infinity Event Center, some of whom at one point tried to rush into the event.
"Do I love the Mormons? I have many friends that live in Salt Lake City -- and by the way, Mitt Romney is not one of them," Trump said to applause. "Are you sure he's a Mormon? Are we sure?"
Romney, the GOP 2012's nominee, said earlier on Friday that he would vote for Ted Cruz
in Utah, who is expected to do well in the state's GOP caucuses on Tuesday. Romney has recently become a leading critic of Trump, the national GOP front-runner, and he said he would back Cruz in Utah because he had the best chance of stopping Trump there.
Trump also said at his campaign rally Friday night that many Mormons had worked for his businesses, and that employees even occasionally make deposits directly to The Church of Jesus Christ of Latter-day Saints so they're not tempted to pocket their paychecks.
"He's out campaigning with (Ohio Gov. John) Kasich
and then he endorses Cruz," Trump added in another shot at Romney. "People say -- are you sure you know what you're doing?"
Romney became at least the third high-profile Republican to have his religion questioned by Trump. Both Cruz, who is Southern Baptist, and former 2016 candidate Ben Carson
, who is Seventh-Day Adventist, have had to reaffirm the particulars of their faith after being questioned by Trump.
And the criticism is particularly harsh for Romney, who has been reluctant to share his Mormon faith in public life. Some Christians do not see Mormonism as a true Christian church.
Protesters try to breach entrance
As Trump was speaking, tensions between Trump supporters and protesters escalated outside the venue. One Trump protester grabbed the hat of a supporter and threw it, and earlier, a Trump supporter shoved a protester who was speaking into a megaphone. As this was happening, dozens of police officers looked on.
At one point, protesters attempted to breach the entrance at the Infinity Event Center as Secret Service officers quickly shut the doors. The protesters were shouting "To the doors," "Chicago" and "Shut it down" before the doors were abruptly closed.
More than 40 police officers in riot gear moved in, creating a standoff between authorities and scores of protesters at the entrance.
The incident, which took place as Trump's event was winding down, caused security inside the venue to direct attendees to leave through a side entrance after the GOP front-runner concluded his remarks. Outside, attendees were directed down a path away from the demonstrations but many from the rally walked over to the protesters and engaged in tense conversations and shouting matches.
Salt Like City police said on Twitter shortly after 9 p.m. local time that no arrests had been made. Det. Cody Lougy told CNN that a "couple hundred" protesters were present out of a crowd of about 500 to 600 people, many of whom were there to support Trump.
But the unrest didn't affect Trump's rally -- which was notable for a lack of protesters inside the center, unlike typical Trump events -- as he mentioned the demonstrators in his speech as part of an observation he made about the "love" in the room.
"There's even some love for the protesters," Trump said to boos. "Honestly, they're doing their thing."
Later Friday, Trump went on Twitter
to praise the "fantastic crowd" inside the event.
"Just leaving Salt Lake City, Utah- fantastic crowd with no interruptions. Love Utah- will be back!" he tweeted.