US Republican presidential front-runner Donald Trump on Saturday blamed supporters of Democratic candidate Bernie Sanders for protests that shut down his Chicago rally, calling the US senator from Vermont "our communist friend".
Trump's Republican rivals, meanwhile, hurled scorn at the New York billionaire, saying he helped create the increasingly tense atmosphere that is now sweeping the race for the White House with his fiery rhetoric.
Trump, who has rallies in Ohio and Missouri on Saturday, canceled the Chicago event on Friday after it turned chaotic, with scuffles breaking out between protesters and backers of the real estate magnate.
The clashes follow a slew of recent incidents of violence at Trump rallies, in which protesters and journalists have been punched, tackled and hustled out of venues, raising concerns about degrading security leading into the Nov. 8 election.
"All of a sudden a planned attack just came out of nowhere," Trump said at a rally in Dayton, Ohio, Saturday morning, calling the protest leaders "professional people".
He said his own fans "were taunted, they were harassed by these other people, these other people by the way, some represented Bernie, our communist friend."
"Now really Bernie should tell his people...he should really get up and say to his people 'stop, stop,'" he said.
A spokesman for Sanders, a self-described Democratic socialist, did not immediately respond to a request for comment.
Earlier on Saturday Trump called the protesters thugs.
"The organized group of people, many of them thugs, who shut down our First Amendment rights in Chicago, have totally energized America!" Trump said on Twitter.
The First Amendment to the US Constitution protects freedom of speech and assembly. The Chicago rally came ahead of five primary elections on Tuesday, including contests in Ohio and Illinois.
Trump rival, US Senator Marco Rubio of Florida, cast wide blame for what he called "third world" images out of Chicago, from the protesters to the media, with his harshest criticism directed at Trump.
"This is a frightening, grotesque, and disturbing development in American politics," he said, speaking to reporters before a rally in Pinellas County, Florida.
John Kasich, the Republican governor of Ohio who is also running for president, told journalists before a campaign event in Cincinnati on Saturday that Trump has created a "toxic environment".
"And that toxic environment has allowed his supporters, and those who seek confrontation, to come together in violence," he said. "There is no place for a national leader to pray on the fears of the people who live in our great country."
In a statement, Republican candidate, US Senator Ted Cruz of Texas, called the incident "sad" and said the protesters should have let the rally happen.
Trump has drawn fervent support as well as criticism for his calls to build a wall along the US-Mexico border and to impose a temporary ban on Muslims entering the country.
His rallies often attract small groups of protesters, but Friday's was the first at which there may have been as many protesters as supporters.
Asked by CNN interviewer Don Lemon if he would take back anything he had said, Trump said: "Now, getting back to before tonight, when I talked about illegal immigration, I have no regrets whatsoever."
"If I didn't bring up illegal immigration, it wouldn't even be a subject of the campaign," he added.
At the University of Illinois-Chicago stadium rally the two sides shouted at each other until a Trump staffer appeared and said the event would be put off until an unspecified date for security reasons.
Police said five people were arrested, including CBS News reporter Sopan Deb. Two officers were injured, with one requiring stitches, police said.
The cancellation followed an appearance by Trump in St. Louis on Friday during which protests forced him to halt his speech repeatedly.
Trump has a significant lead in primary contests over the three remaining Republicans vying for the White House. He is looking to cement it on Tuesday.