  The detection of an astrophysical flux of high-energy neutrinos by IceCube is
a major step forward in the search for the origin of cosmic rays, as this
emission is expected to originate in hadronic interactions taking place in or
near cosmic-ray accelerators. No neutrino point sources, or significant
correlation with known astrophysical objects, have been identified in the
IceCube data so far. The hadronic interactions responsible for the neutrino
emission should also lead to the production of high-energy gamma rays. The
search for neutrino sources can then be performed by studying the spatial and
temporal correlations between neutrino events and very high energy (VHE, E >
100 GeV) gamma rays. We report here on the search for VHE gamma-ray emission
with the H.E.S.S. imaging air Cherenkov telescopes (IACTs) at the reconstructed
position of muon neutrino events detected by IceCube. We will provide an
up-to-date summary of the extensive program to perform prompt IACT observations
of realtime IceCube neutrino event positions. A recent highlight of this
program are the H.E.S.S. observations during the broad multi-wavelength
campaign that followed the detection of the neutrino event IceCube-170922A
arriving from a direction consistent with the location of a flaring gamma-ray
blazar TXS 0506+056 in September 2017. We'll present the H.E.S.S. observations
obtained within ~4h hours of the neutrino detection as well as a complementary
search for gamma-ray emission at longer timescales and put them into the
multi-wavelength and multi-messenger context.
