An Indian man on death row in Pakistan for spying died on Thursday nearly a week after he was attacked by fellow prisoners, who were swiftly charged with murder as New Delhi demanded justice.

Sarabjit Singh, who was sentenced 16 years ago over deadly bombings, died in the early hours as a result of the savage assault in Lahore's Kot Lakhpat jail, a senior doctor at Jinnah hospital in the eastern city told AFP.

The 49-year-old went into a coma after suffering numerous serious injuries when six prisoners attacked him on April 26, hitting him on the head with bricks and fracturing his skull.

Singh's body was flown to India from Lahore in a special aircraft sent by New Delhi, a civil aviation official told AFP on condition of anonymity late Thursday.

Indian foreign ministry spokesman Syed Akbaruddin had earlier said it was "our primary focus" to ensure that Singh's body was returned to India and given a proper burial. He denied that Singh was an Indian spy.

There was anger in India over his death.

"The criminals responsible for the barbaric and murderous attack on Sarabjit Singh must be brought to justice," Indian Prime Minister Manmohan Singh said on his official Twitter page.

Pakistan flags were burned at angry protests in Sarabjit Singh's native Bhikhiwind village, in northern Punjab state.

India complained that its diplomats were denied access to the prisoner as he fought for his life, and the premier said it was "particularly regrettable" that Pakistan had not responded to appeals "to take a humanitarian view of this case."

Pakistan insists regular consular access was granted to Singh and said doctors did everything possible to save him before his death from cardiac arrest.

"The prisoner, who had been in a comatose state and on a ventilator for the last few days, was being provided the best treatment available and the medical staff at Jinnah Hospital had been working round the clock to save his life," the foreign ministry said.

The government provided "all assistance" to Singh's family and the Indian authorities, it added in a statement, and said his body would be handed over "at the earliest possible" time.

AFP