  We report on the experimental observation of internally-pumped parametric
oscillation in a high-Q lithium niobate microresonator under conditions of
natural phase-matching. Specifically, launching near-infrared pump light around
1060 nm into a $z$-cut congruent lithium niobate microresonator, we observe the
generation of optical sidebands around the input pump under conditions where
second-harmonic generation is close to natural phase-matching. We find that a
wide range of different sideband frequency shifts can be generated by varying
the experimental parameters. Under particular conditions, we observe the
cascaded generation of several equally-spaced sidebands around the pump -- the
first steps of optical frequency comb generation via cavity-enhanced
second-harmonic generation.
