According to Moscow, Ukrainian forces recently shot six rockets from a HIMARS launch system at a facility in the eastern Donetsk region where Russian soldiers were stationed.
Two of the missiles were shot down, but four reportedly hit their target resulting in 63 Russian fighters passing away.
The offensive move from Ukraine may be the deadliest attack against Kremlin forces since Putin began his quest to expand Russia last year.
Russian military bloggers, whom the AP calls "largely...reliable during the war," said that ammunition stored close to the facility exploded when the missiles hit, which contributed to the extraordinary number of casualties.
Ukraine seems to have confirmed the attack, admitting to destroying at least 10 Russian military vehicles and saying that "Russian personnel losses were still being clarified."
The governor of Russia's Samara region claimed that an "unspecified number of residents of the region were among those killed and wounded."