The opposition BJP, like Mr Singh's family, had been urging the government to be more firm in its demand that the 49-year-old be sent home for medical treatment. The government's tough talk today is an attempt to deflect the criticism that it will face in an already-stormy parliament session.
"He was murdered in cold blood," said Union minister Manish Tewari. "This is not the manner in which a civilized state treats prisoners in its custody."
In a statement, the Prime Minister said "criminals responsible for the barbaric and murderous attack on Sarabjit must be brought to justice."
Today, the Pakistani government has agreed that Mr Singh's body will be returned to India. His family returned from Pakistan yesterday after being told he was unlikely to recover from his coma and serious brain injuries. His sister, Dalbir Kaur, had castigated the government for not pushing hard enough to have him brought home while he was in critical condition.
Mr Singh had been on death row since 1991 after he was convicted of espionage and links to a series of bombings in the Punjab province of Pakistan.