WASHINGTON • Senator Ted Cruz, a contender for the Republican nomination in the US presidential race, is trying to out-trump rival Donald Trump on immigration, the latest indication of the party's rightward shift on an issue looming large in the race.

The Texan is portraying himself as tougher on illegal immigration than the New York billionaire, who has made immigration a central issue in his campaign.

While campaigning this week in Iowa, Senator Cruz suggested that he would be tougher on people living in the United States illegally than his rival.

"There's a difference," he said in reply to a question over his and Mr Trump's positions on illegal immigrants. "He's advocated allowing folks to come back in and become citizens. I oppose that."

Mr Trump, who saw his standing in the Republican contest rise after endorsing mass deportation of undocumented immigrants, said last July he would let the "good ones" back in through an "expedited process" - a change to the immigration law which requires those deported to wait for up to 20 years before being allowed to return.

Cruz spokesman Catherine Frazier said in an e-mail: "The senator's plan calls for enforcing the law especially with regard to deportations. Same goes for not allowing those who have been here illegally to become citizens."

Mr Trump, firing back during a speech in New Hampshire, suggested the first-term senator had copied his idea to build a wall on the US' southern border.

Senator Cruz also laughed off insinuations by Mr Trump over his eligibility for the top job, dismissing them with a lighthearted tweet implying the remarks were far-fetched.

BLOOMBERG, REUTERS