A two-day incursion from Ukraine into Russia's western borderlands could force the Kremlin to divert troops from front lines as Kyiv prepares a major counteroffensive, and deal Moscow a psychological blow, according to military analysts.

Though Kyiv has denied any role, the biggest cross-border raid from Ukraine since Russia invaded 15 months ago was almost certainly coordinated with Ukraine's armed forces as it prepares to attempt to recapture territory, the experts added.

"The Ukrainians are trying to pull the Russians in different directions to open up gaps. The Russians are forced to send reinforcements," said Neil Melvin, an analyst at the Royal United Services Institute. Ukraine says it plans to conduct a major counteroffensive to seize back occupied territory, but Russia has built sprawling fortifications in its neighbor's east and south in readiness.