US presidential candidate Donald Trump has said the political system is “stacked against me,” and accused the Republican establishment of attempting to deny him the party’s nomination.

“I know the rules very well, but I know it's stacked against me by the establishment,” the billionaire businessman said Tuesday at a CNN town hall meeting in New York City, ahead of New York's Republican primary next Tuesday.

It was the latest in a litany of complaints from Trump after all 37 delegates from Colorado were awarded, without a primary or caucus, to Senator Ted Cruz, his main rival for the Republican presidential nomination.

Trump said the process was “very unfair” and accused Republican leaders of changing the rules to prevent him winning the 1,237 delegates needed to win the nomination outright.

“They changed the rules a number of months ago. You know why they changed the rules? Because they saw how I was doing and they didn't like it,” he said.

'It's not democracy'

“I would have won Colorado. It's not democracy. ... It's such a sad thing that the Republican Party has come to this,” the real estate magnate added.

The comments drew a strong rebuke from the chairman of the Republican National Committee, Reince Priebus. “Nomination process known for a year + beyond. It's the responsibility of the campaigns to understand it. Complaints now? Give us all a break,” he tweeted.

'A disgrace'

During an interview with The Hill, Trump said the nominating process was a “disgrace” for the Republican Party. “Reince Priebus should be ashamed of himself. He should be ashamed of himself because he knows what's going on.”

Observers say that Trump may finish about 80 delegates short of the absolute majority, meaning that the Republican National Convention in July will start without a presumptive nominee.

In that case, campaigns will jockey for advantage and either change or uphold the rules that have governed the primary up until that point. There might be several ballots. Most delegates are pledged to their respective candidates for the first ballot. After that, they can vote for other candidates.

Trump has previously threatened to run as a third-party candidate if the GOP establishment treats him “unfairly.”