Donald Trump launched his harshest attacks yet on presidential rival Ted Cruz in the final days before the South Carolina Republican primary.

"Ted Cruz, I think, is the most dishonest man I've met in politics," Trump said, speaking at a Holiday Inn in Charleston on Monday.

As Trump fights to keep a 20-some point lead over Cruz in the state, each man's campaign is launching frenzied attacks on the other. Cruz is charging that Trump isn't the conservative he claims to be, while Trump says Cruz is lying about his positions on all sorts of issues and is controlled by special interest groups.

"You've got a very unstable guy in Cruz, he's nuts," Trump said, calling the Texas Republican an "absolute disgusting liar."

Trump pushed back against Cruz's recent allegations that he would hurt gun rights, expand abortion access and damage religious freedom by nominating a liberal justice to the Supreme Court. Everything Cruz says about him is the "opposite," the billionaire businessman said.

Trump added that he won't want an "apology" from Cruz on Sunday, the day after the election, for misrepresenting his positions. He pointed to an incident after the Iowa caucuses, where Cruz's campaign mistakenly claimed Ben Carson was dropping out of the election and the senator later apologized.

"His whole deal is he will lie, and after the lie takes place and the election's over, he'll apologize," Trump said.