MOSCOW, May 24 (Reuters) - The Kremlin said on Wednesday (May 24) the use of US-made military hardware by pro-Ukrainian fighters who conducted a raid on a Russian border region this week was testament to the West's growing involvement in the Ukraine conflict.

The Russian military said on Tuesday it had routed militants who attacked the Russian border region of Belgorod with armoured vehicles the previous day, killing more than 70 "Ukrainian nationalists" and pushing the remainder back into Ukraine.

It said it had destroyed four armoured vehicles and five pick-up trucks to repel what was one of the largest incursions onto Russian soil from Ukraine since Moscow launched what it calls its "special military operation" in Ukraine 15 months ago.

Footage of some of the destroyed vehicles released by the Russian defence ministry showed US made military hardware such as Humvee military trucks.

Reuters was able to confirm the location of damaged vehicles and surrounding details shown in the video, though could not verify the date it was filmed.

Russian Defence Minister Sergei Shoigu promised on Wednesday that Moscow would respond to any more cross-border raids by Ukrainian militants swiftly and "extremely harshly."

"It is no secret for us that more and more equipment is being delivered to Ukraine's armed forces," Kremlin spokesman Dmitry Peskov told reporters when asked about the fighters' use of Western-made hardware.

"It is no secret that this equipment is being used against our own military. And it is no secret for us that the direct and indirect involvement of Western countries in this conflict is growing by the day. We are drawing the appropriate conclusions."