US Republican front-runner Donald Trump has warned of riots if he is denied the party's presidential nomination and pulled the plug on a scheduled debate among candidates.
The outspoken New York businessman scored big wins in primaries in Florida, Illinois and North Carolina on Tuesday, bringing him closer to the 1237 convention delegates he needs to win the nomination.
Trump also claimed victory in Missouri but lost the crucial state of Ohio, and left the door open for those in the party trying to stop him from becoming the Republican nominee for the November 8 election.
Trump might fall short of the majority of delegates required, enabling the party's establishment to put forward another name at the July convention in Cleveland to formally pick its candidate.
In an interview with CNN on Wednesday, Trump said the party could not deny him the nomination should he fail to win enough delegates.
"I don't think you can say that we don't get it automatically. I think you'd have riots. I think you'd have riots. I'm representing many, many millions of people."
The party tried to play down his riot comments, only days after Trump supporters and protesters clashed at a rally for the Republican in Chicago that was later scrapped.
"First of all, I assume he is speaking figuratively," Republican National Committee spokesman Sean Spicer told CNN.
Recent outbreaks of violence during protests at Trump rallies have prompted President Barack Obama, a Democrat, and mainstream Republican figures to speak out against the billionaire.
David Farber, a professor of modern American history at Temple University, said although there have been many episodes of violent unrest at American political events, not least the 1968 Democratic convention, Trump's warning of a riot is unprecedented.
In comments likely to raise more concern in the Republican establishment about Trump's lack of experience and temperament, the former reality TV show host said he was for the most part his own foreign affairs adviser.
"I'm speaking with myself, number one, because I have a very good brain," he told MSNBC's Morning Joe show. "I know what I'm doing. ... My primary consultant is myself."
Trump's closest national challenger is first-term US Senator Ted Cruz, who prides himself on being a grassroots conservative often at odds with Republican leaders.
He too warned of severe reactions against an attempt to stage a so-called brokered convention or contested convention to install a Republican candidate supported by party leaders.
"I think that would be an absolute disaster. I think the people would quite rightly revolt," Cruz told CNN.
A brokered convention is a complicated process of sequential votes that opens the way for horse trading.
The Republican establishment's bid to stop Trump may have come too late as the field of candidates has dwindled to only three, with Trump, 69, in command ahead of Cruz, 45, and Ohio Governor John Kasich, 63, who won his state's Republican primary on Tuesday and is the last moderate Republican presidential candidate standing.
Growing in confidence, Trump pulled out of a Republican debate scheduled for Monday in Utah, saying it clashed with a speech he plan to give to a pro-Israel group. Debate hosts Fox News then cancelled the event.
Trump needs to win about 55 per cent of the roughly 1100 delegates still up for grabs in state-by-state nominating contests to guarantee the nomination. It is not an insurmountable challenge.
Republican strategist Ron Bonjean said it might be tough for the party to block Trump at the convention.
"A contested convention would be justified if Trump only had around 35 or 40 per cent of the delegates locked up. However, if he is very close to getting the majority of delegates, it would be politically difficult for the establishment to try stop him by backroom wheeling and dealing without risking a serious backlash from voters," said Bonjean. The strategist is not affiliated with any of the candidates.
