  We report measurements of resistance and ac magnetic susceptibility on FeSe
single crystals under high pressure up to 27.2 kbar. The structural phase
transition is quickly suppressed with pressure, and the associated anomaly is
not seen above $\sim$18 kbar. The superconducting transition temperature
evolves nonmonotonically with pressure, showing a minimum at $\sim12$ kbar. We
find another anomaly at 21.2 K at 11.6 kbar. This anomaly most likely
corresponds to the antiferromagnetic phase transition found in $\mu$SR
measurements [M. Bendele \textit{et al.}, Phys. Rev. Lett. \textbf{104}, 087003
(2010)]. The antiferromagnetic and superconducting transition temperatures both
increase with pressure up to $\sim25$ kbar and then level off. The width of the
superconducting transition anomalously broadens in the pressure range where the
antiferromagnetism coexists.
