Geeta Devi (45), lodged in jail in connection with an abduction case, was rushed to district hospital yesterday after she complained of stomach ache, Jail Superintendent Umesh Singh said.
Devi died during treatment, he added.
However, Devi's family members alleged that during postmortem, injury marks were found on her body, which indicated "atrocities" on her inside the jail.
The police is probing the matter.