Russian and Ukrainian forces are engaged in combat within underground Soviet pipelines near Kupyansk, The Wall Street Journal reported. Russian units are reportedly using old pipelines for covert movement several kilometers to flank Ukrainian positions, a tactic made difficult on the surface by constant drone surveillance.

Ukrainian soldiers are conducting underground operations using ground drones equipped with explosives and remotely controlled weapons. According to Ukrainian commanders, Russia is already preparing special units for underground warfare. WSJ notes that similar combat operations could spread to other sections of the front.