Sushil Koirala, a former Nepalese prime minister and leader of the nation's largest political party, has died in Kathmandu. He was 78.

His doctor, Karbir Nath Yogi, said Tuesday that Koirala died due to complications from pneumonia and respiratory failure.

Koirala was a key figure in the adoption of Nepal's new constitution last September. After ethnic Madhesis later blocked border points with India and imposed a general strike in southern Nepal to protest against the constitution, Koirala attempted to resolve the issue by negotiating with the protesters.

Koirala spent his life in politics fighting for democracy in Nepal and led protests in 2006 that ended a centuries-old monarchy and turned Nepal into a republic.

His politics meant he was always in trouble with the country's kings who had barred political parties since the 1960s, and was jailed for at least six years. He spent 15 years in exile in India because of his opposition to the no-party system imposed by the kings.

He never married and was living in his nephew's house in Kathmandu.

His body was kept initially at the party's headquarters and later moved to the national stadium in Kathmandu for supporters to pay their respects. Hundreds gathered there on Tuesday.

The government said a state funeral will be held on Wednesday and declared a public holiday. Flags will be lowered to half-staff for three days.