Two officials from the Indian High Commission in Islamabad were granted access to Sarabjit yesterday.
They were, however, not allowed to visit him today, the sources said.
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.