A troop carrier idles

A troop carrier idles near a checkpoint close to the Russian-Ukrainian border in Belgorod, Russia, last year.  

KYIV, Ukraine - Russian officials said Tuesday that a counterterrorism operation was underway in the western region of Belgorod, which borders Ukraine, after anti-Russian militias fighting on Ukraine's side in the war mounted an attack on a border post and on an office of the Federal Security Service, or FSB.

The governor of Belgorod, Vyacheslav Gladkov, said Tuesday that one person had died and eight people were injured.