The United States is "sceptical" that the U.S. weapons provided to Ukraine were used in the course of hostilities in the Russian territory of Belgorod, U.S. State Department Spokesman Matthew Miller said during a briefing.

"We've seen some of the reports circulating on social media and elsewhere making claims that U.S.-supplied weapons were used in these attacks. I will say that we're skeptical at this time of the veracity of these reports," the official said.

Miller said Washington does not encourage strikes on Russian territory.

As reported, on May 22 in the Belgorod region began the so-called hostilities, for which the Russian Volunteer Corps (RVC) and the Legion of Freedom took responsibility in order to create a buffer zone of security near the borders of Ukraine.

As of May 23, the formations announced that they had liberated the settlements of Kozinka and Gora-Podil, and also began an assault in Grayvoron.