'I love Latinos,' says Trump at US-Mexico border
Donald Trump greets supporters and tourists at the Trump Tower on July 22, 2015 in New York City

Donald Trump toured the Texas-Mexico border on Thursday to condemn illegal immigration and court Latino voters, but ignited fresh controversy as border agents boycotted his visit.

The real estate mogul and White House contender, who is well ahead of his Republican rivals in most polls, is running an aggressive campaign that has condemned illegal immigration.

He flew into the border town of Laredo in his private jet airliner emlazoned with his name, protecting himself from the harsh sunshine by wearing a white baseball hat with his slogan "Make America Great Again."

"There's nothing more important than what I'm doing," he said on arrival, calling illegal immigration "a huge problem."

He immediately laid into fellow Republican contender Rick Perry, accusing him of doing "a terrible job" as governor of Texas but praising his successor, the Republican Greg Abbott.

The eccentric 69-year-old multi-billionaire caused widespread outrage last month when he accused illegal immigrants from Mexico of importing crime, rape and drugs into the United States.

On Thursday he said he was visiting the border despite being warned it was "dangerous."

Trump said it was only illegal immigrants that he objected to, not Latinos in general. Laredo has a population that is 95.6 percent Hispanic or Latino.

"I employ thousands and thousands of Hispanics," he said. "I love the people. They're great workers. They're fantastic people and they want legal immigration."

But a border patrol union announced a boycott of Trump's visit "after careful consideration of all the factors involved."

The League of United Latin American Citizens also protested Trump's visit.

"Make no mistake, our border with Mexico is not secure and there's no doubt that we need to have an honest discussion about that," said the National Border Patrol Council.

But it said the local branch of the union "does not endorse candidates for any political office."

- Real problem -

Trump hit back quickly and claimed the union had been silenced by superiors in Washington DC "who do not want people to know bad it is on the border."

"They're petrified and afraid of saying what's happening," he told reporters. "They have a real problem here... they invited me and then all of a sudden they were told silencio."

The former reality TV star has hogged the headlines with outlandish remarks and media stunts, lampooning rivals, insulting career politicians and castigating illegal immigrants.

Companies such as Macy's, Univision and NBC have cut ties with Trump, but the mogul has refused to tone down his rhetoric.

On Tuesday, he called rival candidate Senator Lindsey Graham "a total lightweight" and in a stunning breach of etiquette read out Graham's cell phone number and urged people to call him.

Over the weekend, he provoked a backlash among the Republican faithful by trash-talking Vietnam war hero Senator John McCain, one of America's most respected politicians.

McCain, at the time a navy aviator, was held prisoner in Vietnam five years and tortured after being shot down. But Trump was unimpressed.

"He's not a war hero," he said, in remarks that were widely condemned. "I like people that weren't captured, OK?"

But, by ruffling the feathers of the Republican establishment and turning almost all his presidential rivals against him, he has dominated news coverage of the campaign.

His rivals, for their part, have launched counter-attacks -- in part to raise their own profiles in a crowded field of Republican presidential aspirants that now numbers 16.

"Donald Trump's candidacy is a cancer on conservatism, and it must be clearly diagnosed, excised and discarded," Perry said, in particularly harsh remarks on Wednesday.

One recent opinion poll puts him far into the lead in the race for the 2016 Republican nomination, the favorite at 24 percent.

He outpaced his rivals Scott Walker, at 13 percent, and Jeb Bush at 12 percent, according to the Washington Post-ABC News poll.