  We discuss the discovery potential of extended very-high-energy (VHE)
neutrino sources by the future KM3 Neutrino Telescope (KM3NeT) in the context
of the constraining power of the Cherenkov Telescope Array (CTA), designed for
deep surveys of the sky in VHE gamma rays. The study is based on a comparative
analysis of sensitivities of KM3NeT and CTA. We show that a minimum gamma-ray
energy flux of E^2{\phi}_{\gamma}(10 TeV) > 1x10^{-12} TeV cm^{-2} s^{-1} is
required to identify a possible neutrino counterpart with a 3{\sigma}
significance and 10 years of KM3NeT observations with upgoing muons, if the
source has an angular size of R_{src} = 0.1 deg and emits gamma rays with an
E^{-2} energy spectrum through a full hadronic mechanism. This minimum
gamma-ray flux is increased to the level of E^2{\phi}_{\gamma}(10 TeV) >
2x10^{-11} TeV cm^{-2} s^{-1} in case of sources with radial extension of
R_{src} = 2.0 deg. The analysis methods are applied to the supernova remnant RX
J1713.7-3946 and the Galactic Center Ridge, as well as to the recent HAWC
catalog of multi-TeV gamma-ray sources.
