Elon Musk says he is launching a new political party, weeks after dramatically falling out with US President Donald Trump.

The billionaire announced on his social media platform X that he had set up the America Party, billing it as a challenge to the Republican and Democratic two-party system.

However, it is unclear if the party has been formally registered with US election authorities. Musk, who was born outside of the US and is thus ineligible to run for the US presidency, does not say who will lead it.

He first raised the prospect of forming a party during his public feud with Trump, which saw him leave his role in the administration and engage in a vicious public spat with his former ally.

During that row, Musk posted a poll on X asking users if there should be a new political party in the US.

Referencing that poll in his post on Saturday, Musk wrote: "By a factor of 2 to 1, you want a new political party and you shall have it!

"When it comes to bankrupting our country with waste & graft, we live in a one-party system, not a democracy.

"Today, the America Party is formed to give you back your freedom."

As of Saturday, the Federal Electoral Commission had not published documents indicating the party had been formally registered.

While there have been high-profile players outside the traditional two-party system in US politics, it is difficult for them to gain strong enough nationwide popularity to pose a real threat.

In the presidential election last year, candidates from the likes of Libertarian Party, the Green Party and the People's Party all tried in vain to stop Trump or his Democratic rival, Kamala Harris, from winning.

Musk was until recently a core supporter of Trump, dancing alongside him during election rallies last year and bringing his four-year-old son to meet Trump in the Oval Office.

He was also Trump's key financial backer: Musk spent $250m (£187m) to help him regain office.

After the election, he was appointed to lead the so-called Department of Government Efficiency (Doge), which was tasked with identifying swingeing cuts in the federal budget.

His fallout with Trump began when he left the administration in May and publicly criticised Trump's tax and spending plans.

The legislation - which Trump has called his "big, beautiful bill" - was narrowly passed by Congress and signed into law by the president this week.

The massive law includes huge spending commitments and tax cuts, and is estimated to add more than $3tn to the US deficit over the next decade.

Crucially for Musk, who owns electric-vehicle giant Tesla, Trump's bill does not focus on green transition or subsidies for products like Teslas.

"Elon may get more subsidy than any human being in history, by far," Trump wrote on his social media site, Truth Social, this week. "Without subsidies, Elon would probably have to close up shop and head back home to South Africa."

Trump threatened to have Doge look into subsidies in favour of Musk's companies, alluding also to the billionaire's other businesses.

Musk also owns SpaceX, which launches rockets for the US government, and Starlink, which provides satellite service for US and European defence forces.