U.S. Republican presidential front-runner Donald Trump accused his own political party of "ambushing" him during Saturday's presidential debate in South Carolina, and now he's threatening to bolt the GOP and run as an independent.

Trump, who was booed by the audience several times during Saturday's debate, complained that the Republican National Committee (RNC) deliberately packed the venue for the debate with "lobbyists and donors" to pull him down, WND reported.

Trump was visibly angry on Monday when he spoke of the RNC's bid to sabotage his campaign during the South Carolina debate. "I have never met people like politicians. They are the most dishonest people I have ever met. They lie, lie, lie and then they apologise. ... I signed a pledge, but the pledge is not being honoured by them. ... They are in default of their pledge," he said.

Trump was referring to the pledge of allegiance to the Republican Party he signed in September 2015.

Trump issued the threat to run as a third-party candidate five days before the South Carolina primary – a state where he has a commanding lead in the polls and is expected to win easily.

Chad Groover, the chairman of the local Republican Party in Greenville, South Carolina, virtually confirmed Trump's accusation, admitting that he had "a couple of dozen tickets" for the debate and that some of the people in the audience were "donors," WND reported.

Top U.S. radio host and political commentator Rush Limbaugh backed up Trump's claim, saying he had never witnessed such an orchestrated attack on a Republican candidate by the latter's own party.

"[Trump] didn't even have to say anything. He just opened his mouth, a couple of syllables and here came the boos. And it did appear to distract him off the point that he was getting ready to make," said Limbaugh.

"I've never seen anything like that, that I can recall watching intraparty debates ... I've heard a smattering of boos, but I've not seen a whole audience stacked for the expressed purpose. And it was done specifically to make it look like no Republicans in South Carolina like Trump," the conservative radio icon added.

"The [TV] audience was supposed to assume that in South Carolina, the Republican Party hates Trump. That's what they were trying to create, and [Trump] knew it," said Limbaugh.

Also on Monday, Trump said he would seriously consider filing a lawsuit against Texas Sen. Ted Cruz for "false ads" attacking him over eminent domain and a host of other issues.

"One of the ways I can fight back is to bring a lawsuit against him relative to the fact that he was born in Canada and therefore cannot be president," Trump said, WND reported.

Reporters then asked if he would file a lawsuit prior to South Carolina's Feb. 20 primary election.

"Maybe, if I can," Trump replied. He said processing paperwork would not require much time.