WASHINGTON — US President Donald Trump on Sunday called Elon Musk's plans to form a new political party "ridiculous", launching fresh barbs at the tech billionaire who was once his biggest backer.

A day after Musk escalated his feud with Trump and announced the formation of a new United States political party, the Republican president was asked about it before boarding Air Force One in Morristown, New Jersey.

"I think it's ridiculous to start a third party. We have a tremendous success with the Republican Party. The Democrats have lost their way, but it's always been a two-party system, and I think starting a third party just adds to confusion," Trump told reporters.

"It really seems to have been developed for two parties. Third parties have never worked, so he can have fun with it, but I think it's ridiculous."

Shortly after speaking about Musk, Trump posted further comments on his Truth Social platform, saying, "I am saddened to watch Elon Musk go completely 'off the rails', essentially becoming a train wreck over the past five weeks."

Musk announced on Saturday that he is launching the "America Party" in response to Trump's tax cut and spending bill, which he said would bankrupt the country.

"What the heck was the point of @DOGE if he's just going to increase the debt by $5 trillion??" Musk wrote on X on Sunday, referring to the government downsizing agency he briefly led.

Critics have said the bill will damage the US economy by significantly adding to the federal budget deficit. Musk said his new party would in next year's midterm elections look to unseat Republican lawmakers in Congress who backed the sweeping measure known as the One Big Beautiful Bill.

Musk's announcement of a new party immediately brought a rebuke from investment firm Azoria Partners, which said on Saturday it will postpone the listing of its Azoria Tesla Convexity exchange-traded fund because the party's creation posed "a conflict with his full-time responsibilities as CEO". Azoria was set to launch the Tesla ETF this week.

Agencies Via Xinhua