US President Joe Biden has backed striking cars workers in Michigan during a visit to their picket line - a first for a sitting US president.

Mr Biden said that the workers "deserve" raises and other concessions they are seeking.

The visit comes a day before his would-be challenger, Donald Trump, is due to arrive.

But workers told the BBC they felt the rivals might politicise the strike, and urged them to "just stay away".

In brief remarks to the picketing workers on Tuesday, the Democratic president said that they "deserve the significant raise you need and other benefits".

He added that the workers should be doing as "incredibly well" as the companies that employ them.

While US lawmakers - and presidential candidates - frequently appear at strikes to express solidarity with American workers, it is considered unprecedented for a sitting president to do so.

Some workers said they hoped the attention from Mr Biden and his rival would help their cause, but others dismissed the visits as political stunts aimed at getting votes, which would have little practical impact on the negotiations.

"We would much rather neither of them showed up," longtime Ford worker Billy Rowe told the BBC. "We don't want to divide people and when you bring politics into it, it's going to cause an argument."

Earlier in September the UAW declared a strike targeting Ford, General Motors and Stellantis, pushing the three major car companies for better pay and conditions.

The White House, which was heavily involved in resolving a 2022 labour dispute with rail workers, was "not part of the negotiations", White House Press Secretary Karine Jean-Pierre told reporters on Tuesday.

Officials had previously refused to be drawn on whether Mr Biden supports the current UAW proposal, with Ms Jean-Pierre insisting the administration would "leave it to the UAW and the big three".

Mr Biden's presence in Michigan is instead intended to show support to the car workers, Ms Jean-Pierre said.

The president believes "that the men and women of the UAW deserve a fair share of the record profits they've helped to create", she added.

The White House announced Mr Biden's visit to the UAW workers last week, soon after Mr Trump announced he would skip the 27 September Republican presidential debate in California to visit Detroit, the heart of US vehicle manufacturing.

On his social media platform Truth Social, Mr Trump said he had provoked the presidential visit.

"Crooked Joe Biden had no intention of going to visit the United Autoworkers, until I announced that I would be headed to Michigan to be with them [and] help them out," he wrote.

Mr Biden was invited to visit the UAW members by the group's president, Shawn Fain, who has sometimes been critical of Mr Trump.

In his Truth Social post, Mr Trump - who has not been invited by the UAW - vowed that car workers are "toast" if they do not endorse him and if he does not win the election.

On the picket line in Michigan, word of the duelling visits was greeted by groans and "a lot of eye rolls", according to Billy Rowe, 61, one of half a dozen workers huddled in the rain holding picket signs outside a Ford factory near Detroit, receiving regular honks of support from passing cars and trucks.

Mr Rowe, who has worked at Ford for 27 years, said he saw the dispute as one between workers and the companies.

Another Ford employee, Frankie Worley, said that "politics shouldn't be involved" in the issue.

"They come down here and get a picture and say they support us, but really, do they?" said Mr Worley, who has spent 28 years at the company, including 20 on the assembly line. "This involvement is just to put their face against us and say they're helping us. Just stay away."

The strike, he added, is his first. He said he was partly motivated by the fact that his pay has only risen $4 (£3.2) from $28 an hour 25 years ago to $32 today.

"It's hard to make a living now," he said.

The visits by Mr Biden and Mr Trump - currently the frontrunner for the Republican nomination - come as Republicans and Democrats alike focus on the electorally important Midwestern "Rust Belt'', where blue-collar workers such as UAW members form a vital voting bloc.

The battle for those votes in Michigan promises to be intense. Democrats narrowly won the state in the 2020 presidential election after losing there in 2016.

Meanwhile, the UAW endorsed Mr Biden in 2020, but has yet to name a preferred candidate for the 2024 election, saying that the union's support needs to be "earned".

Though the UAW has long been allied with the Democratic party, Mr Worley said that many of its members are upset about issues including inflation and illegal border crossings, weakening support for Mr Biden among the rank-and-file.

"I've seen a big shift," he said.

Mr Biden's visit to the picket line also comes as his administration pushes for more electric vehicle (EV) production in the US - a cause for concern for union members who worry that EVs require fewer workers to build them and could be made in non-union factories for much lower wages.

In a statement issued on Tuesday afternoon, Mr Trump called Mr Biden's visit a "PR stunt" to "distract and gaslight" the US public from other issues, including immigration and public safety.

Surveys suggest that a majority of Americans back the UAW's cause, and a recent Gallup poll found that 67% support unions more generally. (Courtesy, excluding headline, BBC)

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