Ukraine's border guards say they captured a Russian soldier driving to the mainland from Crimea Friday.
Video released by the service show a man wearing military uniform being hand-cuffed and questioned.
Guards say he also had 180 rounds of ammunition and a handgun on him.
He said he was lost.
Crimea's pro-Russian authorities have denied there are any Russian troops on the peninsula outside of a Russian base.
Ukrainian officials and analysts estimate that some 20,000 Russian troops are in Crimea. They say fewer than 12,000 are attached to the Black Sea Fleet.
Crimean's will soon vote on whether to become part of Russia or to choose greater autonomy within Ukraine.
