The US Secret Service is looking into Elon Musk's post on X that suggested it was strange no one attempted to assassinate President Joe Biden or Vice President Kamala Harris, Bloomberg reports.

On Sunday, shortly after the second assassination attempt on former President Donald Trump, an X account called DogeDesigner posed the question, “Why they want to kill Donald Trump?”

Musk responded to his 198 million followers: “And no one is even trying to assassinate Biden/Kamala,” he wrote, adding a ???? at the end of his post.

Musk later deleted the post after it was widely condemned and said it was intended as a joke. But it was already seen by tens of millions, including the US Secret Service.

Threatening the President of the United States is a federal crime and is punishable by up to five years in prison, Bloomberg added.