Police said deceased Sanjib Sarkar, 34, was found dead in the Kendriya Sansodhanagar (central correctional centre) in Bishalgarh (in western Tripura) late Tuesday evening.
"According to jail authorities, Sanjib committed suicide. We are now probing the death," a police official said adding that the issue would be clear once the post-mortem and forensic reports are available.
A truck driver and a resident of Teliamura's Gourangatilla in Khowai district, Sanjib was arrested on August 21 last year in connection with a Narcotic Drugs and Psychotropic Substances (NDPS) case and was in jail since then.
The ruling Bharatiya Janata Party, the opposition Communist Party of India-Marxist, the Congress and other political parties demanded an impartial probe to identify and take action against those responsible for the death.
Maintaining that the incident should not be politicised, BJP spokesman Nabendu Bhattacharjee requested the authorities to take action against the jail guards concerned.
The CPI-M urged the human rights commission to take suo motu notice and fix responsibility in the case.
Senior Congress leader Gopal Roy said that the state's BJP government should institute a probe by a sitting High Court judge into this incident as well as two earlier cases.
On October 31 last year and on January 12 this year, two youths were found dead in police custody in western Tripura and southern Tripura.
( With inputs from IANS )