Elon Musk's SpaceX has laid the groundwork for a move into the US mobile phone market, acquiring a major wireless spectrum deal that could allow its Starlink satellite service to connect directly to ordinary smartphones.

Shares of America's leading mobile operators fell after the announcement. AT&T dropped as much as 7 percent in after-hours trading, while T-Mobile US and Verizon each lost more than 6 percent.

SpaceX said the newly acquired spectrum licences would enable signals to pass through walls and reach conventional devices such as smartphones. Starlink currently delivers high-speed satellite internet, but users on the ground need a dedicated receiver fitted with its own antenna and a clear line of sight to the satellite.

Musk said the acquisition would allow SpaceX to provide coverage across the entire United States, where large areas currently lack access to mobile internet.

Before it can combine its satellite internet service with a terrestrial network, however, SpaceX must first secure approval from the Federal Communications Commission, the country's telecommunications regulator.

The spectrum was sold by investment firm Green Management. The purchase price was not immediately disclosed.