Factbox-What do we know about the Ukrainian New Year's Eve attack on Russian troops?

Workers remove debris of a destroyed building purported to be a vocational college used as temporary accommodation for Russian soldiers, 63 of whom were killed in a Ukrainian missile strike as stated the previous day by Russia's Defence Ministry, in the course of Russia-Ukraine conflict in Makiivka (Makeyevka), Russian-controlled Ukraine, January 3, 2023. REUTERS/Alexander Ermochenko

MAKIIVKA, Ukraine (Reuters) - A Ukrainian missile strike on Jan. 1 against a vocational school in the Russian-controlled Donetsk region of Ukraine housing mobilised Russian troops has become one of the bloodiest incidents of Russia's nearly year-long war in Ukraine.

What do we know, and what do we not know, about what happened?