Two officials from the Indian High Commission in Islamabad were granted access to Sarabjit on Satuday. They were, however, not allowed to visit him on Sunday, the sources said. Denying access, Pakistan said hospital has been now declared as a sub-jail, said sources.
It was immediately not clear what action India will take in this regard.
49-year-old Sarabjit is currently in a coma and on ventilator in an ICU in Jinnah Hospital.
Doctors have been working to revive him since he was attacked in Kot Lakhpat Jail on Friday. His skull was fractured and he sustained injuries to his face, neck and torso during the assault. He was convicted for alleged involvement in a string of bombings in Pakistan's Punjab that killed 14 people in 1990.