Indian national Sarabjit Singh, currently on death row in a Lahore jail, was on Friday seriously injured on the head and rushed to a hospital for an emergency surgery after being attacked by two prisoners.
Sarabjit was admitted to the intensive care unit of the state-run Jinnah Hospital on Friday evening, Indian and Pakistani officials told PTI.
The attack occurred when Singh and other prisoners were brought out of their cells for an hour-long break.
The two prisoners assaulted Sarabjit with blunt objects and he sustained a severe head injury.
Sarabjit was initially taken to the hospital within the prison. After his condition worsened, he was moved in an ambulance to Jinnah Hospital, officials in Lahore said.
A CT scan was performed on Sarabjit and doctors were scheduled to perform a surgery, official sources said.
"Singh suffered a serious head injury and we are going to operate on him to save his life," said a senior doctor.
The superintendent and assistant superintendent of Kot Lakhpat Jail and personnel deputed to guard Sarabjit were suspended after the incident, TV news channels reported.
Foreign Office spokesman Aizaz Ahmad Chaudhry told the media that officials of Kot Lakhpat Jail were probing the incident.
Chaudhry said the Foreign Office was examining a request from the Indian High Commission seeking consular access to Sarabjit.
Officials of Kot Lakhpat Jail refused to speak to the media, saying they were not authorised to comment on the matter.
Journalists were barred from approaching the ward in which Sarabjit was being treated in Jinnah Hospital.
Police commandos and intelligence operatives were deployed to guard the ward.
Ministry of External Affairs spokesperson Syed Akbaruddin said that India has sought consular access.
"India has contacted the ministry of foreign affairs in Pakistan for ascertaining the facts. Two officers have been sent to Lahore for consular access and we are awaiting their response. We are in touch with the foreign ministry and the Presidency," Akbaruddin said.
Sarabjit's lawyer Owais Sheikh said, "Yes, this is very much disturbing. This is not something that we can ignore. Naturally, this will have very, very serious consequences.
"Whatever has happened, our jail authorities are responsible for that. Hope god saves Sarabjit Singh. He has been seriously hurt," he said.
Human Rights activist Ansar Burney said, "I am going to file another mercy petition to the Pakistan President to immediately release him and send him to India".
The Kot Lakhpat Jail currently has nearly 17,000 prisoners though its official capacity is only 4,000.
There have been instances in the past of prisoners being attacked and even killed within the prison.
Authorities had tightened Sarabjit's security after the recent execution of Afzal Guru, who was convicted of involvement in the 2001 terror attack on the Parliament.
Sarabjit was convicted for alleged involvement in a string of bomb attacks in Punjab province that killed 14 people in 1990.
His mercy petitions were rejected by the courts and former President Pervez Musharraf.
The outgoing Pakistan Peoples Party-led government put off Sarabjit's execution for an indefinite period in 2008.
Sarabjit's family says he is the victim of mistaken identity and had inadvertently strayed across the border in an inebriated state.