Russia's military is likely a reluctant participant in Ukraine's conflict, the top U.S. military officer said on Thursday, July 24, adding that although he had not spoken to his Moscow counterpart in about two months he was keeping an open line of communication, Reuters reported.

"I think the Russian military and its leaders that I know are probably somewhat reluctant participants in this form of warfare," General Martin Dempsey said, noting Russia's use of both conventional forces along the border and of proxies inside the country.

His comments came as the United States accused Russia of firing artillery across its border with Ukraine to target Ukrainian military positions in the conflict with pro-Russian armed groups.

"I think it does change the situation," Dempsey said, speaking at a security forum in Aspen, Colorado. He added that instead of de-escalating, Russia's president Vladimir Putin has "actually taken a decision to escalate."

Dempsey, chairman of the Joint Chiefs of Staff, voiced concerns about the implications of Russia's actions on its ties with the United States and with Europe.

"My real concern is that having lit this fire in an isolated part of eastern Europe, it may not stay in eastern Europe. And I think that's a real risk," Dempsey said.

"I'm keeping an open line of communication with my counterpart and he's doing the same with me."