  Tibet AS-gamma collaboration has recently reported detection of gamma-rays
with energies up to Peta-electronvolt from parts of the Galactic plane. We
notice that the analysis of gamma-ray flux by the Tibet AS-gamma experiment
also implies an upper bound on the diffuse gamma-ray flux from high Galactic
latitudes(|b|>20 degrees) in the energy range between 100 TeV and 1 PeV. This
bound is up to an order-of-magnitude stronger than previously derived bounds
from GRAPES3, KASCADE and CASA-MIA experiments. We discuss the new
TibetAS-gamma limit on high Galactic latitude gamma-ray flux in the context of
possible mechanisms of multi-messenger (gamma-ray and neutrino) emission from
nearby cosmic ray sources, dark matter decays and large scale cosmic ray halo
of the Milky Way.
