The Kremlin said on Friday that it was already aware of attempts by Ukraine to strike targets on Russian territory with weapons provided by the United States.

Kremlin spokesman Dmitry Peskov was commenting after four U.S. officials told Reuters on Thursday that U.S. President Joe Biden had quietly authorised Kyiv to launch U.S.-supplied weapons at military targets inside Russia that are supporting an offensive against the northeastern Ukrainian city of Kharkiv.

"No, nothing is known to us about this particular decision," Peskov told a news briefing when asked about it.

"What we know is that generally, there are already attempts to strike Russian territory with weapons produced by the United States. This is enough for us and it speaks volumes about the degree to which the United States is involved in the conflict."

Peskov did not elaborate on his assertion about such strikes or reference evidence detailing them.

He said a pro-war mood was also being whipped up in Europe to the point of "pre-war hysteria".