Bahraini authorities ordered Saturday an investigation into the "beating and death" of an inmate in custody, the interior ministry said.
The ministry did not reveal the name of the prisoner but activists of the Shiite majority named him online as Hassan al-Sheikh, saying that he died of torture at Jaw Prison.
Interior Minister Sheikh Rashid bin Abdullah al-Khalifa has ordered an "internal review after the public prosecution's investigation into the beating and death of an inmate," said a statement.
The review will include all policies and procedures followed in prisons, it said.
"The death of the man, thought to have been at the hands of three ministry personnel, was irresponsible, unjustified and unacceptable," a statement cited the minister as saying, insisting that it was an "individual and isolated act."
Hundreds of Shiites have been arrested and faced trial after a month-long uprising was quelled in March 2011. Jaw Prison is known to host scores of them.
Shiite protesters continue to frequently clash with security forces in villages outside the capital Manama.
The Sunni-ruled monarchy is a strategic archipelago just across the Gulf from Iran and home to the US Navy's Fifth Fleet.