Gupta told IANS that Bhullar was sent to a mental asylum around two and a half years ago, and has since been lodged there.
"As per Indian law, a convict cannot be hanged till he is declared mentally and physically fit," Gupta told IANS, unmindful of the irony.
"When we get Bhullar's fitness certificate from the asylum, he will be lodged back in Tihar Jail and hanged, as per procedure," he said.
The Supreme Court Friday rejected the mercy plea of Khalistani terrorist Bhullar, convicted and sentenced to death in 2003 for carrying out a bomb blast outside the Indian Youth Congress office in Delhi in 1993, leaving nine people dead.
Bhullar had sought commutation of his death penalty to life sentence on the ground that there was inordinate delay by the president in deciding on his mercy plea.
He had approached the Supreme Court in 2011.