The Republican front-runner in the race for US president, Donald Trump, on Saturday was interrupted by protesters during campaign rallies in Ohio one day after security concerns forced him to back out of an appearance in Chicago.

A man tried to storm the stage while the billionaire businessman addressed a rally in the south-western town of Vandalia, according to media reports. Trump flinched when the protester tried to climb onto the stage from behind him as he addressed a crowd of several thousand.

Broadcast video showed security guards immediately surrounding the candidate and fending off the man, who was arrested, according to local broadcaster WDTN.

Later in Cleveland, Ohio, security officers had to escort protesters who tried to disrupt Trump's speech out of an arena. Trump taunted the protesters as the were shown the door, saying, "Hey look it's a Bernie person," referring to US Senator Bernie Sanders, one of his Democratic rivals. "Get your people in line, Bernie."

Sanders campaign said there was no evidence any Sanders' staff was involved in organizing the protests and called Trump a "pathological liar."

The incidents at Trump's campaign rallies followed a volatile situation Friday night in Chicago, where fighting broke out between anti-Trump protesters and supporters of the candidate, prompting Trump to cancel the rally.

Trump critics say his own statements at campaign rallies in recent weeks have fanned the flames and helped escalate the situation at his events to violence. He blamed not only Sanders, but also Democratic front-runner Hillary Clinton for sending the protesters into his events.

"It is Clinton and Sanders people who disrupted my rally in Chicago," Trump said on Twitter, referring to them as "Phony politicians."

Clinton called Trump's rhetoric "political arson." She said Trump's "ugly, divisive rhetoric" and encouragement of violence "is wrong, and it's dangerous."

Trump's rivals also were out stumping on Saturday ahead of crucial votes on Tuesday in five states - Illinois, Missouri, Ohio, Florida and North Carolina. If Trump's momentum continues, he will be in the best position of the four Republican candidates still in the race to capture the GOP nomination.

Voting took place Saturday on two US territories, the Mariana Islands and Guam, the state of Wyoming and Washington, DC. Clinton won the Marianas, which was contested only by Democrats, with 54 per cent, claiming her 14th victory overall.

Cruz finished ahead in Guam and was leading in Wyoming with 58 per cent with about two-tirds of the vote counted, according to the New York Times. Results from Washington were expected later Saturday.

Much of the attention on Tuesday will be on the states of Ohio and Florida because they have the most delegates.

US Senator Marco Rubio, whose campaign has struggled to pick up momentum in recent weeks, campaigned in his home state of Florida.

In an interview with the New York Times he compared Trump to a "third-world dictator" and said he was "leading the country dangerously close to a boiling point."

Ohio Governor John Kasich, campaigning in Ohio, didn't mention Trump, but said there was no place in US politics for a national leader to "prey on the fear of the people."

Both Rubio and Kasich's chances of continuing in the race hinge on their performance in their home state's on Tuesday. They will be under intense pressure to quit if they don't win.

US Senator Ted Cruz, Trump's nearest rival, said Trump's campaign "affirmatively encourages violence" and that has created an environment that encourages "nasty discourse." He said he intended to "carry a message of unity that brings people together rather than to divide."

In an interview with CNN on Friday, Trump said he had no intention of causing any violence at his rallies.

He later said on Twitter that the group of people who appeared at the Chicago rally with plans to disrupt it had "shut down our First Amendment rights" and had "totally energized America!"

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