US presidential candidate Donald Trump cancelled a rally in Chicago after rowdy shouting matches broke out between the flamboyant billionaire's supporters and opponents.
Backers of the Republican frontrunner and protesters inflamed by his candidacy later shoved and punched each other at the University of Illinois in Chicago where the rally had been scheduled to take place on Friday.
The announcement that Trump would postpone the rally prompted some of the crowd inside the Chicago Pavilion to break out into cheers of, "We stopped Trump!"
But, in boisterous scenes, supporters of the candidate chanted back: "We want Trump! We want Trump!"
Scuffles broke out as signs were ripped from hands and police moved in to quickly defuse the most serious incidents.
There were also isolated clashes outside the venue, according to media reports.
The full statement from Trump's campaign read: "Mr Trump just arrived in Chicago and after meeting with law enforcement has determined that for the safety of all of the tens of thousands of people that have gathered in and around the arena, tonight's rally will be postponed to another date.
"Thank you very much for your attendance and please go in peace."
However, a spokesman for the Chicago Police Department told the Associated Press news agency that it had not recommended Trump take such a step.
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Before the announcement, highly charged exchanges had taken place between Trump supporters and protesters as the crowds waited for his arrival.
Veronica Kowalkowsky, an 18-year-old Trump supporter, said before the event that she had no ill will towards the protesters - but didn't think they felt the same way.
"I feel a lot of hate," she said. "I haven't said anything bad to anyone."
Ted Cruz responded to the cancellation by saying that Trump had created "an environment that encourages this sort of nasty discourse".
Black Lives Matter
Earlier in the day, at a rally in St. Louis, Missouri, Trump had been speaking for less than 10 minutes when protesters began interrupting him. The disruptions continued over the next hour as Trump urged security to "get them out".
"Can I be honest with you, it adds to the flavour, it's more exciting. Isn't this better than listening to a long boring speech?" Trump said of the disruptions.
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At some events, altercations have turned physical. In New Orleans last week, several protesters supporting the Black Lives Matter movement were dragged out as Trump shouted "get them".
In Fayetteville, North Carolina, on Wednesday, protesters interrupted Trump's speech more than 16 times.
One was punched by a member of the crowd as he was led from the arena.
Trump has become a particularly polarising candidate in the presidential campaign.
He has both inspired impassioned supporters and ignited a backlash of angry dissent with his promise to build a wall along the US-Mexican border to keep out illegal immigrants and his call to temporarily ban the entry of non-US Muslims into the country.