A statement from the prisoners, published by the banned Al-Wefaq opposition group, first reported the hunger strike in Jau prison which holds dissidents detained during a 2011 crackdown on Shiite-led protests.
The Britain-based Bahrain Institute for Rights and Democracy (BIRD) said “hundreds of political prisoners” are taking part.
Bahraini authorities have downplayed the incident, saying that “some inmates… returned their meals on August 8” at the prison near a southeastern village.
The General Directorate of Reform and Rehabilitation said “the health and safety of all inmates is a priority and… all inmates have the same access to primary and secondary care as all citizens in Bahrain”.
But in the statement published by Al-Wefaq on Monday, the inmates said they were kept in their cells for 23 hours a day. They called for proper medical care, access to education and permission to pray together at a prison mosque.
“For many years, political prisoners have endured degrading treatment and prolonged confinement in cells alongside the systematic denial of medical treatment,” said BIRD advocacy director Sayed Ahmed Alwadaei.
Audio recordings of prisoners confirming the hunger strike were posted by activists on social media.
“I am worried for my father’s life,” Maryam al-Khawaja, daughter of one of the inmates on strike, told AFP in an emailed statement.
“I don’t want my father to be released to us in a coffin,” said Khawaja, whose father has been detained for 12 years and is allegedly being denied medical treatment.
Bahrain is a key regional ally of the United States and is home to the US Navy’s Fifth Fleet.
It has imprisoned scores of dissidents since 2011, when authorities backed by a Saudi military force crushed Shiite-led protests demanding a constitutional monarchy and an elected prime minister.