Sanaullah Ranjay, also called Sanaullah Haq, died at the PGI Hospital in Chandigarh, in northern India, of multiple organ failure after being in a coma since last Friday, his doctors said, the Hindustan Times reported.
Haq, a convicted terrorist serving a life sentence, was taken to the hospital from a Jammu jail where he was injured, CNN-IBN reported.
Reports said he was attacked to avenge the death of Indian prisoner Sarabjit Singh in a Pakistani jail after being similarly attacked by Pakistani inmates. The death of Singh, who had been convicted of spying, set off strong reactions in India when relations between the South Asian neighbors were already tense due to the November 2008 terror carnage in Mumbai, which India says was planned in Pakistan. The Mumbai attacks killed 166 people.
Indian Home Minister Sushil Kumar Shinde said Haq's body would be handed over to Pakistan, CNN-IBN reported.
The report, citing sources, also said an autopsy on Haq's body would be conducted in Chandigarh.
A statement on Haq's death issued by Pakistan's Ministry of Foreign Affairs on its website said he had "succumbed to the brutal injuries" suffered during the jail attack.
"We have conveyed our concern to the government of India in this regard and demanded that an investigation into the incident be held and perpetrators of this heinous crime be brought to justice," the statement said.
The statement said Pakistan's prime minister also called on the Indian government "to ensure the safety and security of all Pakistani prisoners in Indian jails."
CNN-IBN quoted an Indian External Affairs Ministry spokesman that India would provide assistance in returning Haq's body to Pakistan.
The ministry official also said India has proposed that officials from the two countries meet to work on the recommendations of a judicial committee calling for humane treatment of prisoners.
The Times of India reported that Pakistani consular officials had been granted access to Haq, who was arrested in 1996 and convicted of involvement in a bombing near a Hindu shrine in Kashmir in 1994 in which 10 people dead.