"All of us shouldn't even have answered that question," Kasich said of the pledge party officials asked all the candidates to sign in September.

"No, I don't anymore," Trump said, when asked by CNN's Anderson Cooper if he continued "to pledge to support whoever the Republican nominee is?"

Trump said he has "been treated very unfairly" by the Republican National Committee and party establishment figures. The billionaire front-runner accused rival Cruz of "essentially saying the same thing" in response to a question about the pledge.

Earlier, Cruz had told Cooper when asked the same question: "I'm not in the habit of supporting someone who attacks my wife and my family ... I think nominating Donald Trump would be an absolute trainwreck, I think it would hand the general election to Hillary Clinton."

Trump said Cruz "doesn't need to support me, I have tremendous support right now from the people."

"I don't really want him to do something he's not comfortable with," he said.