Donald Trump called immigrants in the United States illegally "animals" and "not human" in a speech in Michigan on Tuesday, resorting to the degrading rhetoric he has employed time and again on the campaign trail.

The Republican presidential candidate, flanked by several law enforcement officers, listed several criminal cases involving suspects in the country illegally in often graphic terms and warned that violence and chaos would consume America if he did not win the Nov. 5 election.

While speaking of Laken Riley - a 22-year-old nursing student from Georgia allegedly murdered by a Venezuelan immigrant in the country illegally - Trump said some immigrants were sub-human.

"The Democrats say, 'Please don't call them animals, they're humans.' I said, 'No, they're not humans, they're not humans, they're animals,'" said Trump, president from 2017-2021.

During stump speeches, Trump frequently claims that immigrants crossing the border with Mexico illegally have escaped from prisons and asylums in their home countries and are fueling violent crime in the United States.

While available data on criminals' immigration status is sparse, researchers say people living in the U.S. illegally do not commit violent crimes at a higher rate than native-born citizens.

Biden blames Trump for encouraging Republicans not to pass legislation in Congress this year that would have beefed up security at the southern border and introduced new measures aimed at reducing illegal immigration.

"Donald Trump is engaging in extreme rhetoric that promotes division, hate and violence in our country," Michael Tyler, Biden campaign communications director, told reporters on Tuesday ahead of Trump's speech.

"He encourages white nationalists and cheers on the disgusting behavior of the extreme far right," Tyler said.

Trump delivered his speech, titled "Biden's border bloodbath" in the city of Grand Rapids, where police said 25-year-old Ruby Garcia was murdered last month in her car by Brandon Ortiz-Vite, 25, who she was dating. Ortiz-Vite was in the country illegally, police said.

The murders of Garcia and Riley have allowed Trump's campaign to simultaneously play to fears among some Americans about violent crime and immigration.

Some 38 per cent of Republicans cited immigration as the country's top issue in a Reuters/Ipsos poll released in late February, as did about one in five independents.

Trump frequently claims without evidence that migrants have caused a spike in violent crime in U.S. cities. On Tuesday, he repeated an unfounded claim that Latin American nations are intentionally sending their criminals into the United States.

Tuesday's primaries

Trump was due to hold a rally with supporters in Green Bay, Wisconsin, after his Michigan speech. Michigan and Wisconsin are two swing states that could determine whether Biden or Trump occupies the White House next year.

In the 2020 election, Biden beat Trump in Wisconsin by less than one percentage point, and in Michigan by less than three. Both states are expected to be extremely close again this year.

Although both Trump and Biden have mathematically clinched their presidential nominations, they will be on their party's presidential primary ballots in Wisconsin on Tuesday.

The Biden team will be watching for protest votes by Democrats angry over the president's strong support of Israel in its war against Hamas in Gaza.

In February's presidential primary in Michigan, a state with a large Muslim population, Biden easily won the primary but more than 100,000 Democrats voted "uncommitted," instead of for Biden, as a protest over his Gaza policy.

A similar option is available in Wisconsin on Tuesday. The "uncommitted" campaign's goal is to get 20,682 voters to mark their ballots "uninstructed," Wisconsin's version of "uncommitted." The number is significant. Biden beat Trump by that number in the state in 2020.

(Reporting by Tim Reid and Nathan Layne, additional reporting by Nandita Bose; editing by Ross Colvin and Howard Goller)