  We report the first observation of the doubly-strange baryon $\Xi(1620)^0$ in
its decay to $\Xi^-\pi^+$ via $\Xi_c^+ \rightarrow \Xi^- \pi^+ \pi^+$ decays
based on a $980\,{\rm fb}^{-1}$ data sample collected with the Belle detector
at the KEKB asymmetric-energy $e^+ e^-$ collider. The mass and width are
measured to be 1610.4 $\pm$ 6.0 (stat) $^{+5.9}_{-3.5}$ (syst)~MeV$/c^2$ and
59.9 $\pm$ 4.8 (stat) $^{+2.8}_{-3.0}$ (syst)~MeV, respectively. We obtain
4.0$\sigma$ evidence of the $\Xi(1690)^0$ with the same data sample. These
results shed light on the structure of hyperon resonances with strangeness
$S=-2$.
