In one of the worst assaults on the Kremlin's forces since the war started more than 10 months ago, Ukrainian forces launched rockets at a facility in the eastern Donetsk region where Russian soldiers were stationed, killing 63 of them, according to Russia's military ministry on Monday.

According to a statement from the defense ministry, two of the six rockets fired by Ukrainian forces using a HIMARS launch system were shot down. The strike's date was not specified.

The strike, using a US-supplied precision weapon that has proven critical in enabling Ukrainian forces to hit key targets, delivered a new setback for Russia which in recent months has reeled from a Ukrainian counteroffensive.

The Ukrainian military has not directly confirmed the strike, but seemed to acknowledge what appeared to be the same attack that Russian authorities reported.