The United States has not seen evidence that troops from close Russian ally Belarus are in Ukraine, the Pentagon said Friday.

"We haven't seen any indications that Belarusian troops or forces have moved inside Ukraine," Pentagon spokesman John Kirby told reporters.

"We're not tracking any imminent involvement by Belarusian forces," Kirby said. "That's not to say that it couldn't happen or that it wouldn't happen."

The Pentagon spokesman said the United States had noted comments by Belarusian President Alexander Lukashenko that his country's forces would "come to the defense of the rear of Russian forces should they be attacked."

Pentagon spokesman John Kirby said the US has not seen any indications Belarusian troops are in Ukraine
Pentagon spokesman John Kirby said the US has not seen any indications Belarusian troops are in Ukraine GETTY IMAGES via AFP / Kevin Dietsch

"That's the first time that he's ever said anything about Belarus perhaps getting involved," Kirby said, but there are "no indications at this time that they have or that that's in the offing."

A senior US defense official said earlier Friday that Russian forces have launched more than 80 missiles into Ukraine from Belarus.

That represents about 10 percent of the more than 800 Russian missiles fired into Ukraine since the invasion began, the official said.

Russian troops have fired nearly 400 missiles from inside Ukraine while just under half have been fired from Russia, the official said.