Imphal, Aug. 22: Former Manipur chief minister and Rajya Sabha MP Rishang Keishing died today at the age of 96 following multiple-organ failure.

The Manipur government has declared a three-day mourning in the state.

Keishing was declared dead by doctors at the Regional Institute of Medical Sciences here around 8.15pm. He had been admitted to the hospital on July 1 because of age-related health problems.

A senior leader of the Congress, Keishing served as the chief minister of Manipur for four times, besides stints in the Lok Sabha and the Rajya Sabha.

He was the chief minister of Manipur from 1980 to 1988 and from 1994 to 1997. He was the last surviving member of India's first post-1947 Parliament and the oldest serving parliamentarian in the world. His Rajya Sabha term ended on April 9, 2014.

Keishing was born to Rungdi and Mungshingla Keishing at Bungpa village in Ukhrul district of Manipur on October 25, 1920. He did his graduation from St Paul's College, Calcutta. He married Khatingla Keishing on April 15, 1950 and has four sons and two daughters.

He joined the Congress under the leadership of Pandit Jawaharlal Nehru and remained a member of the AICC since then. He was elected to the Lok Sabha from Outer Manipur parliamentary constituency in 1952. He was first sworn in as chief minister on November 27, 1980. In 2001, when 13 of the 14 Congress MLAs defected from the party, Keishing stood alone but firm as a disciplined Congress MLA in the Opposition bench. After three months, the ministry fell and the Assembly was dissolved. In the subsequent elections, the Congress came back to power.

His body was brought to his home at Mantripukhri, on the outskirts of Imphal, where floral tributes were paid. The body will be taken to Manipur PCC office tomorrow where party leaders will pay their respects. The body will be taken to his native village in Kamjong subdivision on Thursday for the burial.

Manipur chief minister Biren Singh tweeted: "I am deeply shocked & full of grief to hear news of demise of pabung Sh Rishang Keishing. Manipur lost a true son of soil. RIP."

The Congress tweeted, "Condole the passing of former CM of Manipur & Rajya Sabha MP Shri Rishang Keishing. Our prayers and thoughts with his family."

West Bengal chief minister Mamata Banerjee tweeted: "Saddened at the passing of Rishang Keishing a long-serving CM of Manipur in the 1980s, former RS MP. Condolences to his family & wellwishers."