President Donald Trump on Sunday called it "ridiculous" that his former ally and billionaire Elon Musk has created a new political movement to challenge the "one-party system" in the United States.

On Saturday, Musk, the world's richest man who has become a fierce critic of Trump, said he founded what he called the"Party of America."

“I think it’s ridiculous to create a third party,” the Republican president told reporters before boarding his plane to Washington. “It’s always been a two-party system, and I think creating a third party only contributes to the confusion.”

“Third parties have never worked. So we can have fun with that, but I think it's ridiculous,” Trump added.

Musk and the US president were until recently close allies. The tech billionaire, head of Tesla, SpaceX, and the social network X, was the Republican's top donor in 2024.

But the duo engaged in a bitter dispute over the president's mega-tax bill, passed by Congress and which Musk called"explosive" for US debt.

The billionaire, who has been a U.S. citizen since 2002, vowed to do everything in his power to ensure that the lawmakers who voted for the law lose their seats.

In a post on his Truth Social platform, Trump later Sunday called his former ally"a complete mess" and a "mess over the last five weeks."

He wrote that the creation of a third party would cause “complete and total disruption and chaos.”

Earlier, US Treasury Secretary Scott Bessent also took aim at him by suggesting that his companies would urge him to focus on business rather than politics.

"I think the boards of their companies would like him to run them again, because he's better than anyone at it," Bessent said when asked on CNN if Musk's announcement concerned the government.

"I imagine those boards of directors didn't like yesterday's announcement and will encourage him to focus on his business activities, not politics," he added.

Bessent said that the principles of the so-called Department of Government Efficiency (DOGE), which Musk led for several months as part of Trump's efforts to cut government spending and the federal government, are"very popular," but "if you look at the polls, Elon wasn't."