Republican presidential contender Mitt Romney, seeking to protect his lead and fend off challenges from rivals in this early voting state, assailed Rudy Giuliani and Mike Huckabee over supporting tuition breaks and broader sanctuary for illegal immigrants or their children.

At the same time, GOP candidate Rep. Tom Tancredo, running far behind Romney and other Republicans in opinion polls, is airing an ad in New Hampshire taking sharp aim at illegal immigration as a border security issue.

Romney, the former Massachusetts governor, likened Huckabee and Giuliani to Democratic front-runner Hillary Clinton, saying Tuesday, "There are those people in both parties who are in a sanctuary state of mind, who believe in sanctuary cities, who believe in policies which are sanctuary in nature."

In campaign appearances and advertisements in Iowa and elsewhere, Romney is increasingly using illegal immigration to differentiate himself from the rest of his opponents. The issue is particularly salient in Iowa's ultra-conservative western region, given the influx of immigrants coming to work in fields and factories in recent years.

Romney contended that Huckabee, the former Arkansas governor, fought for tuition breaks for children of illegal immigrants in his state, while Giuliani, the former New York mayor, provided tuition breaks at the City University for illegal immigrants. He said that Clinton, too, backs such breaks.

"Giving a better deal to the children of illegal aliens than we give to U.S. citizens from surrounding states is simply not fair and not right," Romney told reporters during a one-day visit.

In turn, Huckabee said in a phone interview with The Associated Press: "The attacks from a guy who has sanctuary cities in his state is interesting." Huckabee said he backed a bill in Arkansas -- and would do so again -- that gave children of illegal immigrants "the opportunity to be awarded for academic achievements" based on merit provided they were in the process of applying for citizenship.

"Why would you penalize the children for the crime of the parents?" Huckabee asked.

Also responding to Romney, Giuliani spokeswoman Maria Comella accused him of ignoring his own record as governor while he campaigns for president. "Under Gov. Mitt Romney the number of illegal immigrants skyrocketed, while he recommended millions of dollars in state aid to numerous sanctuary cities and to companies employing illegal immigrants, not to mention the illegals working on his own lawn," she said.

During his time as governor, at least three Massachusetts cities offered sanctuary to illegal immigrants.

Tancredo, running on an anti-immigration message, is airing an ad in Iowa that casts border security as a defense against terrorism. The ad opens with a man in a hooded sweatshirt and a backpack in a crowded mall. An explosion is heard as the screen goes dark. And the ad then displays clips of the aftermath of terrorist acts in Europe, including a picture of a bloodied child.

"There are consequences to open borders beyond the 20 million aliens who have come to take our jobs," a narrator says. "Islamic terrorists now freely roam U.S. soil, jihadists who froth with hate, here to do as they have in London, Spain, Russia. The price we pay for spineless politicians who refuse to defend our borders against those who come to kill."

Tancredo, who has long advocated tight limits on immigration, barely registers in public opinion polls. But the immigration issue does resonate. Sen. John McCain, who helped lead an effort to overhaul immigration laws and provide a path to citizenship for some immigrants, lost momentum last spring as the debate over the legislation played out in Congress.

The powerful image of a hooded terrorist plays to viewers' post-9/11 fears. It is reminiscent of Lyndon Johnson's "Daisy" ad in 1964 against Barry Goldwater, which suggested a Goldwater presidency could result in nuclear war.

"I approve this message because someone needs to say it," Tancredo says at the beginning of the ad.

His Web site opens to the ad with a direct appeal for contributions: "Please help us keep this important statement on the air: Donate now".