Why is the Kremlin acknowledging the losses?

Russia has admitted suffering the deadliest strike on its troops sine Putin launched his full-scale invasion of Ukraine ten months ago. The Kremlin has confirmed that 63 of its soldiers were killed in a series of strikes on a temporary barracks in the eastern Donetsk region. 
The Ukrainian defense forces have claimed responsibility for the New Year's Eve attack and say the true death toll is much higher.
Russian media have sharply criticized the senior officers involved.