Chronicle of Great Patriotic War... writes:
at the dawn 9 Pe-2 bombed Luostari. From 9 Pe-3 which were flying to bomb Banak four were attacked by enemy fighters (near Ischma?) and didn't return from sortie.
No unit is given for both groups, but this webpage claims that second group was from 121. BAP (and gives names of people involved):
http://igor-ktb.livejournal.com/5765.html