The US Defense Department has signed a contract with billionaire Elon Musk's satellite communication service to help Ukraine maintain vital internet access.

Starlink provides high-speed internet access via a network of satellites owned by SpaceX, a venture led by Musk. Ukraine has used the system to enable its reconnaissance drones to track and attack Russian forces.

The Defense Department said in a statement on Thursday, "We continue to work with a range of global partners to ensure Ukraine has the resilient satellite and communication capabilities they need."

It also said, "Satellite communications constitute a vital layer in Ukraine's overall communications network."

SpaceX has been offering Starlink to Ukraine free of charge since the start of the Russian invasion. But Musk said last October that his firm could not afford to do so indefinitely, given the massive costs involved.