Donald Trump. REUTERS/David Becker

LAS VEGAS (AP) -- Donald Trump railed Saturday against efforts by some frustrated Republicans planning a last-ditch effort to try to thwart him from becoming the party's nominee, threatening at one point to stop fundraising if Republicans don't rally around him.

Speaking at a theater 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 organize 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."

Trump also wondered 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 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.

Donald Trump. REUTERS/David Becker

"I'd love to do it," said Trump, who has been holding fundraisers across the county this week largely benefiting the Republican National Committee. "You know, life is like a two-way street."

A Republican National Committee spokesman did not immediately respond to a request for comment.

Trump's event drew several thousand people, but many seats remained empty when Trump began speaking because of security screening delays. Even after he took the stage, the line of supporters circled the slot machines on the casino floor. Tourists carrying beer and wearing bikinis watched the crowds with amusement.

Trump mistakenly blamed the delays on the Transportation Security Administration, which sometimes handles audience screening but was not involved in screening at the Treasure Island hotel. Casino security, metro police and the Secret Service were handling those efforts at the Las Vegas event.

"I'm not happy about it, but I have to put up with it," Trump told supporters after erroneously blaming the TSA. "They didn't bring enough machines."

Trump has stepped up his criticism of President Barack Obama in the wake of the Orlando nightclub shooting. In Las Vegas, he told supporters: "If you think Orlando was the end of it with this weak attitude and this pathetic president we have, it wasn't, folks."

He also offered a warning: "You are going to have problems the likes of which you've never seen unless Donald Trump becomes your president."