Trump wants Republicans behind him

Donald Trump has railed against some Republicans planning a last-ditch effort to try to thwart him from becoming the party's nominee, threatening to stop fundraising if Republicans don't rally around him.

Speaking at a theatre at the Treasure Island hotel on the Las Vegas strip, Trump referred to "an insurgent group" trying to deny him delegates at the party's July convention.

"Now you have a couple of guys that were badly defeated and they're trying to organise maybe like a little bit of a delegate revolt," he said.

"I thought they already tried that."

Trump pushed back against such efforts several times during his speech, claiming they were somehow "illegal" and then dismissing them as a media-generated fabrication.

"It's all made up by the press," he said. "It's a hoax, I'm telling you."

While Trump dismisses the effort as invented, more Republicans in Congress are saying they will not attend the party convention and are not endorsing his candidacy.

Meanwhile, a movement exists among some conservative delegates and operatives to change party rules to allow a different nominee, though it's a longshot effort lacking sufficient backing and a candidate to offer up at an alternative.

Indeed, Trump wondered aloud who his opponents would pick as a replacement, a problem that has plagued the "Never Trump" movement for months.

"Who are they going to pick? I beat everybody. But I don't mean beat - I beat the hell out of them," he said.

Trump has continued to face resistance from Republicans who have voiced increasing concern over his inflammatory rhetoric. And he appeared increasingly frustrated on Saturday, saying, "It would be helpful if the Republicans could help us a little bit."

The billionaire businessman also threatened that, if Republicans don't come together, he was prepared to stop fundraising and go back to largely self-funding his campaign.

"I'd love to do it," said Trump.