"Sean Dummy is trying to kill NASA!" the billionaire entrepreneur said in a post on X, referring to Sean Duffy, who also serves as US transportation secretary.

On Monday, Duffy announced that NASA was seeking new bids to support its mission to return humans to the Moon, citing delays in the development of SpaceX's Starship rocket amid a space race with China.

"I love SpaceX. It's an amazing company. The problem is, they're behind. They pushed their timelines out and we're in a race against China," Duffy said on Fox News.

The US space agency's Artemis program hopes to return humans to the Moon as China forges ahead with a rival effort that is targeting 2030 at the latest for its first crewed mission.

After several postponements, NASA is now planning the Artemis 3 mission for mid-2027, but experts say SpaceX must still clear complex technical challenges before its rocket is ready.

Duffy later said on X that the United States is "in a race against China so we need the best companies to operate at a speed that gets us to the Moon FIRST."

He mentioned potential bids from Jeff Bezos's Blue Origin, "and others."

On X, Musk retorted, "SpaceX is moving like lightning compared to the rest of the space industry.

"Starship will end up doing the whole Moon mission. Mark my words," he said.

The tension is ratcheting up amid questions over who will become the permanent leader of NASA.

Trump had originally tapped businessman Jared Isaacman, a Musk associate, but the White House suddenly withdrew the nomination in May, just before Musk's relationship with Trump soured.

Media reports suggest that Trump is again considering Isaacman, while Duffy is hoping to hold on to the NASA position.

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