By Anne KauranenIMATRA, Finland (Reuters) - Finland is building the first stretch of a fence on its border with Russia on Friday, less than two weeks after it joined the NATO military alliance to complete a security U-turn taken in response to the war in Ukraine. Until now, the Finnish-Russian border has been a mere line in the vast forests covering the area, marked only by a low wire fence intended to stop cattle and other domestic animals but not people. We construct the target areas which are accessible by vehicle and where large-scale illegal immigration is likely," Tolppanen said