The attack caught the Ukrainian troops unaware as the TOS-1A units managed to reach the firing position undetected and unleashed their deadly payload of thermobaric rockets during nighttime.
With the fortified positions they were occupying suddenly transformed into raging infernos, the Ukrainian soldiers had no chance to escape and ended up perishing in the ensuing conflagration.
This short video released by the Russian Ministry of Defense shows how this attack took place.