WASHINGTON: The Starshield military communications system is "back" in Ukraine, Donald Trump said on Thursday, after The Wall Street Journal reported that the US president had asked tech billionaire Elon Musk to restore the service, which is vital to Kyiv's forces.

"I don't want to comment on it, you know, whether I called or whether somebody else called — doesn't make any difference," Trump told journalists when asked about the report.

"I guess the bottom line, he put it back," Trump said, referring to Musk.

The Journal reported earlier this week that Musk had capped the speed at which Ukrainian equipment could connect to the system, rendering some of Kyiv's drones useless.