Image copyright EPA Image caption Mr Trump said 'riots' are possible if he wins the most delegates but still is not the Republican nominee

Presidential hopeful Donald Trump has said his supporters would "riot" if he was denied the Republican nomination despite winning the popular vote.

Some Republicans have signalled that they would be open to a brokered convention, where party officials, not voters, would chose the nominee.

That would only take place if Mr Trump fell short of the 1,237 delegates needed to secure the nomination.

It is unclear if he can hit that threshold before the convention.

"I'm representing a tremendous - many, many millions of people, in many cases first-time voters," Mr Trump, the front-runner, told CNN. "If you disenfranchise those people ... I think you would have problems like you've never seen before," he said.

Mr Trump has at least 646 delegates and is favoured to win many coming contests, but challenges from opponents Texas Senator Ted Cruz and Ohio Governor John Kasich have blunted his momentum.

On Tuesday, Mr Trump won primaries in four states - Florida, Illinois, Missouri and North Carolina. Yet a win by Mr Kasich in Ohio raised the possibly that Trump's delegate count could fall short.

Mr Cruz, who is currently in second place in the race, is also opposed to a brokered convention.

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Mr Cruz currently has 397 delegates and Mr Kasich has 142.

Florida Senator Marco Rubio, once thought to be a promising Republican choice for nominee, dropped out of the race on Tuesday after a poor showing in state primaries.

Mr Trump also said he would not be participating in a Fox News Republican debate set for 21 March in Salt Lake City, Utah.

Mr Kasich's campaign said they would not participate if Mr Trump did not, so the network then cancelled the debate.

The billionaire businessman with no prior political experience has come under fire by his fellow Republican candidates, along with Democrats, for encouraging a culture of violence at his campaign rallies.

Criticism over violent Trump rallies

He called off a rally to be held in Chicago after clashes between protesters and supporters.

He has said no one gets hurt at his "love-fest" rallies and that he denies responsibility for any violence.