Donald Trump has called for racial profiling to combat terror in the United States.

The technique uses ethnicity, race or religion as a means to determine whether someone is likely to commit a crime. In an interview on Sunday the presumptive Republican nominee said it was "not the worst thing to do" as he repeated his call to keep mosques under surveillance.

"I think profiling is something that we're going to have to start thinking about as a country," Trump told CBS's Face the Nation. "You look at Israel and you look at others and they do it successfully.

"You know, I hate the concept of profiling. But we have to start using common sense and we have to use, you know, we have to use our heads."

The technique is outlawed in the European Union but there have been a number of reports that suggest people with Arabic or non-Jewish names travelling in Israel are stopped and checked more often than Israeli Jews.

In the aftermath of the Orlando terror attack that killed 49 in a gay nightclub, the New York billionaire repeated his call on a ban on Muslims entering the US.

Earlier on Sunday he also said he supported restrictions on gun control advocated by President Obama and Democrat candidate Hilary Clinton. The proposal, which will be voted on in the Senate on Monday, would ban the sale of guns to people on terror and no-fly lists.

"I'd like to see that," Trump told ABC. "It's just simpler."

He said he understood the concern of many Republicans about civil liberties but sided with most Democrats in supporting the measure.

"It could be that people are on there that shouldn't be," he said, but added: "We have to make sure that people that are terrorists or have even an inclination toward terrorism cannot buy weapons, guns."

His comments came as House Speaker Paul Ryan made it clear he would not stop a rebellion against Trump's nomination for President. The official announcement will be made at the Republican's national convention in July but most of the party's delegates strongly oppose Trump. As the most senior Republican in Congress, Ryan will chair the convention where the delegates will announce their candidate.

"They [the delegates] write the rules, they make the decisions," he told NBC's Meet the Press. "All I want to make sure is to make sure it is done above board, clearly, honestly and by the rules."

He added: "I see my role, now that he's got the plurality [of delegates], he actually won, is pretty much a ceremonial position. But the last thing I am going to do is weigh in and tell delegates what to do."