Russian forces have taken four border villages in Ukraine’s northeastern Sumy region, a local official said on Tuesday, days after Russian President Vladimir Putin said he had issued an order to establish a buffer zone along the border.

Sumy borders Russia’s Kursk region, where a surprise Ukrainian incursion last year captured a pocket of land in the first occupation of Russian territory since World War II. Creating a buffer zone could help Russia prevent further Ukrainian cross-border attacks there. Meanwhile, the Russian bombing campaign reduced overnight.