Republican presidential candidate Donald Trump has threatened to send his supporters to the campaign rallies of Democrat Bernie Sanders, showing no sign of toning down his rhetoric after clashes erupted at his own events over the weekend.
Trump, front-runner for the Republican nomination, appeared unchastened after simmering discord between his supporters and protesters angry over his positions on immigration and Muslims turned into a palpable threat on Friday.
He was forced to cancel a Chicago rally on Saturday.
Trump blamed supporters of Democratic candidate Sanders for the incidents in Chicago, where scuffles broke out between protesters and backers of the real estate magnate. He called the US senator from Vermont "our communist friend".
On Sunday, he went a step further in an early morning post on Twitter: "Bernie Sanders is lying when he says his disruptors aren't told to go to my events. Be careful Bernie, or my supporters will go to yours!"
The scenes in Chicago followed several weeks of violence at Trump rallies, in which protesters and journalists have been punched, tackled and hustled out of venues, raising concerns about security leading into the November 8 presidential election to replace Democratic President Barack Obama.
The disturbances continued on Saturday at a Trump rally in Dayton, Ohio, where Secret Service officers scrambled to surround the candidate after a man charged the stage.
Trump scheduled rallies on Sunday in Illinois, Ohio and Florida before the next five presidential nominating contests on Tuesday, which could cement his lead over Republican rivals US Senators Ted Cruz and Marco Rubio and Ohio Governor John Kasich.
Sarah Palin, who ran as vice president in Republican John McCain's failed 2008 campaign against Obama, planned to stump for Trump in Florida.
Trump, who has harnessed the discontent of white, working class voters angry over international trade deals that cost them jobs, has made his opposition to the 1993 North American Free Trade Agreement and proposed 12-nation Trans-Pacific Partnership a centerpiece of his campaign.