Republican presidential candidate Donald Trump has claimed there are "a lot of bad genes" in the United States while discussing murders allegedly committed by immigrants living illegally in the United States.

"How about allowing people to come to an open border, 13,000 of which were murderers," Trump said in an interview with conservative commentator Hugh Hewitt, while discussing the immigration policies of his Democratic opponent in the November 5 election, Vice President Kamala Harris.

"Many of them murdered far more than one person, and they're now happily living in the United States. You know, now a murderer, I believe this, it's in their genes. And we got a lot of bad genes in our country right now."

The former president has frequently attacked migrants on the campaign trail, particularly those who have been implicated in crimes. 

At times, he has used dehumanising language, and he has increasingly turned to extremely graphic depictions of the crimes even though a range of studies show immigrants do not commit crime at a higher rate than native-born Americans.

Trump appeared to be referring to a letter from Immigration and Customs Enforcement to Republican Representative Tony Gonzales, released in September, which showed that 13,099 people have been convicted of homicide who are on ICE's "non-detained docket".

That docket includes various types of immigrants who entered the country legally and illegally.

(US Vice President Kamala Harris during a visit to the US-Mexico border in September. AP PHOTO)

A spokesperson for the Department of Homeland Security called those statistics misleading.

"The data in this letter is being misinterpreted," the spokesperson wrote in an email. 

"The data goes back decades; it includes individuals who entered the country over the past 40 years or more, the vast majority of whose custody determination was made long before this Administration. 

"It also includes many who are under the jurisdiction or currently incarcerated by federal, state or local law enforcement partners."

In a statement, the Trump campaign defended his comments, saying he was speaking only about murderers, not immigrants.

"President Trump was clearly referring to murderers, not migrants," Trump campaign press secretary Karoline Leavitt said. 

"It's pretty disgusting the media is always so quick to defend murderers, rapists, and illegal criminals if it means writing a bad headline about President Trump."

The White House condemned Trump's remarks.

"That type of language is hateful, it's disgusting, it's inappropriate, and it has no place in our country," White House spokesperson Karine Jean-Pierre said.

By Gram Slattery in Washington, D. C.