(Reuters) -Authorities in four Russian regions bordering Ukraine and in Russian-controlled Crimea announced they were stepping up security measures on Monday over what they said were “possible provocations” from the Ukrainian side. Moscow, which sent thousands of troops into Ukraine in what it calls a “special military operation”, has accused Ukraine of targeting its border regions, including by striking a fuel depot in the city of Belgorod earlier this month. The authorities in the Belgorod, Voronezh, Bryansk and Krasnodar regions and in Crimea said they were boosting security and urged citiz…