With government refusing to share classified information under RTI about former Prime Minister Lal Bahadur Shastri's death, his family has demanded that all doubts be cleared on the mystery shrouding it.

"His death was a very big shock to us and the entire nation. I was just 16 years old then. But I remember his body had darkish blue spots on the chest, abdomen and back. My mother and we suspected he died under mysterious circumstances," Shastri's son Sunil said.

He said the doubts about Shastri's death persists in the minds of millions across the country.

"I personally feel Shastri was not just a great leader but a national treasure. He was a lovable person who many feel was the best Prime Minister India had. The government should come out with the facts about his death and close the chapter once and for all," Sunil said.

After Shastri's death in Tashkent, USSR, on January 11, 1966 soon after signing the Tashkent Pact with Pakistan, his wife Lalita had alleged that he was poisoned. A query was posed under the Right to Information Act about his death but the government has refused to part with classified information on the issue.

Sunil Shastri said there was no reason for the government to hide facts about his father's death.

"There is a doubt in our minds about his death. Wherever I go, people ask me about his mysterious death. The government should not hesitate in sharing the information about his death," he said.

Recalling the day when his father's body was brought to India, Sunil said the family's reaction was that the death was "mysterious and raised doubts".

The Prime Minister's Office, while refusing information under the RTI Act on the cause and circumstances of Shastri's death, has said revealing these details could harm India's foreign relations and would violate Parliamentary Privilege.

Anuj Dhar, author of CIA's Eye on South Asia, had filed the RTI plea on the issue.

The government has admitted that no post-mortem was conducted on Shastri. However, his personal doctor R N Chugh and some Russian doctors conducted a medical examination.

The Russian butler attending on Shastri at the time of his death was arrested for suspected poisoning but released later.

It was maintained that Shastri had died of cardiac arrest but his family insisted he was poisoned.

The PMO has stated that it has a document on Shastri's death but has refused to divulge the details.