U.S. Republican presidential candidate Donald Trump on Monday rejected a barrage of criticism from his own party over his allegations of bias against a Hispanic judge, insisting his concerns were valid.

"All I want to do is figure out why I'm being treated unfairly by a judge. And a lot of people agree with it," Trump said on Fox News.

Trump has been on the defensive since his comments last week about Mexican-American U.S. District Judge Gonzalo Curiel, who is overseeing fraud lawsuits against Trump University, the New York businessman's defunct real estate school.