Israeli officials say a 27-year-old Palestinian has died in an Israeli prison.
Raed Hamad was found dead in his cell late Friday, and his lawyer says an autopsy is being planned.
The Palestinian Prisoner Affairs minister, Issa Karake, said on Saturday that the prisoner had been in solitary confinement for the last 18 months and that this worsened his condition.
Hamad's lawyer, Tareq Barghouth, said his client required psychological help but none was provided during his five years in detention.
Israel has nearly 6,700 Palestinians in custody, and their release is a key Palestinian demand. Tens of thousands have been held over the years.
Hundreds marched in the West Bank on Saturday to mark an annual "prisoners' day."