"I think there is some confusion. First, it is not a case of pardon. More importantly, it is not Sarabjit. It is Surjeet Singh, son of Sucha Singh. His death sentence was commuted in 1989 by President Ghulam Ishaq Khan on the advice of then prime minister Benazir Bhutto," presidential spokesman Farhatullah Babar was quoted as saying by Geo News.
Law Minister Farooq Naek Tuesday told the interior ministry that Surjeet Singh had completed his life term in jail and should be released and sent back to India, Babar said.
Keeping him in jail any longer will be illegal confinement, he said.
It would be entirely "out of context" to mention President Asif Ali Zardari in the matter, Babar said.
Surjeet Singh is reportedly being held in Kot Lakhpat Jail in Lahore. He has been in a Pakistani prison for over 30 years, after being arrested near the border on charges of spying during the regime of military ruler Zia-ul-Haq.
Media reports Tuesday said Zardari had converted Sarabjit Singh's death sentence to life imprisonment and ordered authorities to release him if he had completed his prison term.
Sarabjit Singh's family claim he had crossed into Pakistan inadvertently in August 1990 in an inebriated state and was arrested there.
But Pakistani police say Sarabjit Singh, who is known as Manjit Singh there, was involved in acts of terrorism. A resident of Bhikhiwind township along the border, Sarabjit has been languishing in Pakistani jails since then.
He was convicted of staging four bombings in Lahore and Multan in 1990 that killed at least 14 people.