The role of Elon Musk's SpaceX in an ambitious new U.S. missile defense system is in question following the dramatic feud last week between the billionaire entrepreneur and President Donald Trump, according to three people familiar with the project.

Following escalating tensions between President Trump and Elon Musk, the White House has directed the Defense Department and Nasa to scrutinize SpaceX's multi-billion dollar contracts. This review, prompted by Musk's criticisms of Trump,