WASHINGTON (AFP) - House Speaker Paul Ryan on Tuesday described Donald Trump's criticism of a Mexican-American judge as "racist," but reiterated his support for the presumptive Republican presidential nominee.

Trump claims that federal Judge Gonzalo Curiel, who is handling a lawsuit against the now-defunct Trump University, is biased against him because of his Mexican heritage.

Trump has come under criticism by fellow Republicans for his remarks against Curiel, who was born in the United States of Mexican parents.

"Claiming a person cannot do the job because of their race is sort of like the textbook definition of a racist comment," Ryan told reporters.

"I think that should be absolutely disavowed. It's absolutely unacceptable."

Ryan, however, quickly pivoted to attack the likely Democratic presidential candidate and offer support for Trump.

"But do I believe that Hillary Clinton is the answer? No, I do not. Do I believe that Hillary Clinton is going to be the answer to solving these problems? I do not.

"I believe that we have more common ground on the policy issues of the day, and we have more likelihood of getting our policies enacted with him than we do with her," Ryan said of Trump.

Trump, who says he wants to build a wall on the border with Mexico, asserted in a interview published Thursday that Curiel has "an absolute conflict" of interest because of his "Mexican heritage" and because he is a member of a Mexican-American lawyers association.

Ryan, the most senior elected Republican official in the country, announced his support for Trump only last week.