Donald Trump has called for more racial profiling by US law enforcement agencies in a move that risks further stoking a growing Republican rebellion against his presidential candidacy.
Already facing widespread criticism over his response to last week's mass shooting in Orlando, the presumptive nominee refused to back down and instead urged more scrutiny of American Muslims.
Racial profiling is the controversial practice of targeting individuals for suspicion of crime based on their ethnicity or religion and has been widely opposed as discriminatory by the civil liberties groups.
"I think profiling is something that we're going to have to start thinking about as a country," Mr Trump told CBS's Face The Nation. "You look at Israel and you look at others, and they do it and they do it successfully. And you know, I hate the concept of profiling, but we have to start using common sense."
He also revived a call for surveillance of mosques, a proposal that has already been widely condemned. "If you go to France right now, they're doing it. In fact, in some instances they're closing down mosques," he said.
Mr Trump's latest remarks marked an extension of his hard-line response to last Sunday's killing of 49 people in a gay night club by Omar Mateen, an American Muslim born in New York. He said the massacre justified a suspension of immigration from countries with "a proven history of terrorism".
The billionaire property tycoon also provoked unease among Republican officials by tweeting his thanks for "congratulations" on being right about terrorism and later tried to link President Barack Obama to the killings by suggesting that he sympathised
with radical jihadists. Mateen pledged allegiance to the Isil during the attack.
Mr Trump's racial profiling comments seem certain to increase anxiety about his candidacy amid renewed plots by party officials to unseat him as their nominee at next month's showcase convention in Cleveland.
Mr Trump issued an appeal for party unity following disclosures that delegates were trying to organise an "anyone but Trump" movement that could overturn his expected nomination despite his emphatic victory in the Republican primaries.
Opinion surveys showed a majority of Americans disapproved of Mr Trump's response to the Orlando shootings. One poll showed 70 per cent of voters registering a negative view of the candidate. The revolt is being spearheaded by officials with power to change the rules at the convention. "This literally is an 'anybody but Trump' movement," Kendal Unruh, a Republican delegate from Colorado told the Washington Post. "Nobody has any idea who is going to step in and be the nominee, but we're not worried about that. We're just doing that job to make sure that he's not the face of our party."
More ominously for Mr Trump, Paul Ryan, the Republican speaker of the House of Representatives - who has given the candidate a tepid endorsement - said he would not use his position as chairman of the convention to save his nomination if delegates wanted to remove him.
"It's not my role to tell delegates what to do and what not to do," he told NBC's Meet The Press programme. "They write the rules and make the decisions."
He also said he would not try to persuade Republicans who felt they could not back Mr Trump, saying: "I'm not going to tell someone to go against their conscience."
Mr Trump dismissed the growing disquiet, calling attempts to change the convention rules "illegal".